GE 211 Programming in C++ Array &Matrix Dr. Ahmed Telba.

GE 211 Programming in C++

Array &MatrixDr. Ahmed Telba

Initializing an Array

• DataType ArrayName[dimension] = { element1, element2, …, elementn};• examples of declaring an initializing arrays:• int number[] = {18, 42, 25, 12, 34, 15, 63, 72, 92, 26, 26, 12};• double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};

#include <iostream>using namespace std;

int main(){

double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};

cout << "2nd member = " << distance[1] << endl;cout << "5th member = " << distance[4] << endl;

return 0;}

• This would produce:• 2nd member = 720.52• 5th member = 6.28


int main(){

double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};

cout << "Distance 1: " << distance[0] << endl;cout << "Distance 2: " << distance[1] << endl;cout << "Distance 3: " << distance[2] << endl;cout << "Distance 4: " << distance[3] << endl;cout << "Distance 5: " << distance[4] << endl;

return 0;}

• This would produce:• Distance 1: 44.14• Distance 2: 720.52• Distance 3: 96.08• Distance 4: 468.78• Distance 5: 6.28

// You can use such a constant in a for loop to scan the array and access each of its members. Here is an example:


int main(){

const int numberOfItems = 5;double distance[numberOfItems] = {44.14, 720.52, 96.08, 468.78, 6.28};

cout << "Members of the array\n";for(int i = 0; i < numberOfItems; ++i)

cout << "Distance " << i + 1 << ": " << distance[i] << endl;

return 0;}

In both cases, this would produce:Members of the arrayDistance 1: 44.14Distance 2: 720.52Distance 3: 96.08Distance 4: 468.78Distance 5: 6.28

Filling Up an Array

When you declare an array without initializing it, we have mentioned that the compiler reserves an amount of memory space for the members of the array. But that is only what the compiler does. Each part of such reserved space is filled with garbage. Therefore, you must make sure that you know the value held by a member of the array before making any attempt to process the value held by that member of the array. Consider the following example:


int main(){

const int numberOfItems = 5;double distance[numberOfItems];


return 0;}

This would produce:Distance 1: -9.25596e+061Distance 2: -9.25596e+061Distance 3: -9.25596e+061Distance 4: -9.25596e+061Distance 5: -9.25596e+061


int main(){

const int numberOfItems = 5;double distance[numberOfItems] = {44.14, 720.52, 96.08};


return 0;}

• This would produce:• Distance 1: 44.14• Distance 2: 720.52• Distance 3: 96.08• Distance 4: 0• Distance 5: 0


int main(){

const int NumberOfItems = 5;double distance[NumberOfItems] = {44.14, 720.52, 96.08, 468.78, 6.28};

cout << "Distance 1: " << distance[0] << endl;cout << "Distance 2: " << distance[1] << endl;cout << "Distance 3: " << distance[2] << endl;cout << "Distance 4: " << distance[3] << endl;cout << "Distance 5: " << distance[4] << endl;cout << "Distance 6: " << distance[5] << endl;cout << "Distance 7: " << distance[6] << endl;cout << "Distance 8: " << distance[7] << endl;

return 0;}

This would produce:Distance 1: 44.14Distance 2: 720.52Distance 3: 96.08Distance 4: 468.78Distance 5: 6.28Distance 6: 2.64214e-308Distance 7: 2.12414e-314Distance 8: 1.00532e-307

Operations on Arrays#include <iostream>using namespace std;

int main(){

// We know that we need a constant number of elementsconst int max = 10;int number[max];

// We will calculate their sumint sum = 0;

cout << "Please type 10 integers.\n";

for( int i = 0; i < max; i++ ){

cout << "Number " << i + 1 << ": ";cin >> number[i];sum += number[i];

}

cout << "\n\nThe sum of these numbers is " << Sum << "\n\n";

return 0;}

This would produce:Please type 10 integers. Number 1: 120 Number 2: 42 Number 3: 75 Number 4: 38 Number 5: 904 Number 6: 6 Number 7: 26 Number 8: 55 Number 9: 92 Number 10: 20

The sum of these numbers is 1378

// A 2-Dimensional arraydouble distance[][4] = {

{ 44.14, 720.52, 96.08, 468.78 },{ 6.28, 68.04, 364.55, 6234.12 }

};using namespace std;int main(){

// A 2-Dimensional arraydouble distance[2][4] = {44.14, 720.52, 96.08, 468.78, 6.28, 68.04, 364.55, 6234.12};// Scan the array from the 3rd to the 7th membercout << "Members of the array";cout << "\nDistance [0][0]" << ": " << distance[0][0];cout << "\nDistance [0][1]" << ": " << distance[0][1];cout << "\nDistance [0][2]" << ": " << distance[0][2];cout << "\nDistance [0][3]" << ": " << distance[0][3];cout << "\nDistance [1][0]" << ": " << distance[1][0];cout << "\nDistance [1][1]" << ": " << distance[1][1];cout << "\nDistance [1][2]" << ": " << distance[1][2];cout << "\nDistance [1][3]" << ": " << distance[1][3];

cout << endl;return 0;

}

This would produce:Members of the arrayDistance [0][0]: 44.14Distance [0][1]: 720.52Distance [0][2]: 96.08Distance [0][3]: 468.78Distance [1][0]: 6.28Distance [1][1]: 68.04Distance [1][2]: 364.55Distance [1][3]: 6234.12

Multidimensional Arrays[0][0] [0][1] [0][2] [0][3] [0][4][1][0] [1][1] [1][2] [1][3] [1][4][2][0] [2][1] [2][2] [2][3] [2][4]int anArray[3][5] ={{ 1, 2, 3, 4, 5, }, // row 0{ 6, 7, 8, 9, 10, }, // row 1{ 11, 12, 13, 14, 15 } // row 2};

Matrix addition code #include <iostream>void mult_matrices(int a[][3], int b[][3], int result[][3]);void print_matrix(int a[][3]);void main(void){ int p[3][3] = { {1, 3, -4}, {1, 1, -2}, {-1, -2, 5} }; int q[3][3] = { {8, 3, 0}, {3, 10, 2}, {0, 2, 6} }; int r[3][3]; mult_matrices(p, q, r); cout<<_matrix(r);}

void mult_matrices(int a[][3], int b[][3], int result[][3]){ int i, j, k; for(i=0; i<3; i++) {

for(j=0; j<3; j++) { for(k=0; k<3; k++) {

result[i][j] = a[i][k] + b[k][j]; } }

}}void print_matrix(int a[][3]){ int i, j; for (i=0; i<3; i++) {

for (j=0; j<3; j++) { printf("%d\t", a[i][j]); } printf("\n");

}}

#include <stdio.h>

void add_matrices(int a[][3], int b[][3], int result[][3]);void print_matrix(int a[][3]);

void main(void){ int p[3][3] = { {1, 3, -4}, {1, 1, -2}, {-1, -2, 5} }; int q[3][3] = { {8, 3, 0}, {3, 10, 2}, {0, 2, 6} }; int r[3][3];

add_matrices(p, q, r);

printf("\nMatrix 1:\n"); print_matrix(p);

printf("\nMatrix 2:\n"); print_matrix(q);

printf("\nResult:\n"); print_matrix(r);}

void add_matrices(int a[][3], int b[][3], int result[][3]){ int i, j; for(i=0; i<3; i++) {

for(j=0; j<3; j++) { result[i][j] = a[i][j] + b[i][j]; }

}}void print_matrix(int a[][3]){ int i, j; for (i=0; i<3; i++) {

for (j=0; j<3; j++) { printf("%d\t", a[i][j]); } printf("\n");

}}

Matrix addition

initialization of Two-Dimensional Array

• An two-dimensional array can be initialized along with declaration. For two-dimensional array initialization, elements of each row are enclosed within curly braces and separatedby commas. All rows are enclosed within curly braces.

Referring to Array Elements

• To access the elements of a two-dimensional array, we need a pair of indices: one forthe row position and one for the column position. The format is as simple as:name[rowIndex][columnIndex]

Arrays example #include <iostream> using namespace std; int billy [] = {16, 2, 77, 40, 12071}; int n, result=0; int main () { for ( n=0 ; n<5 ; n++ ) { result += billy[n]; } cout << result;system("pause"); return 0; }

Multidimensional arrays

• Multidimensional arrays can be described as "arrays of arrays". For example, a bidimensional array can be imagined as a bidimensional table made of elements, all of them of a same uniform data type.

• int jimmy [3][5];

#define WIDTH 5 #define HEIGHT 3 int jimmy [HEIGHT][WIDTH]; int n,m; int main () { for (n=0;n<HEIGHT;n++) for (m=0;m<WIDTH;m++)

{ jimmy[n][m]=(n+1)*(m+1); } return 0; }• jimmy[1][3]

•#define HEIGHT 3

• #define HEIGHT 4

// arrays as parameters #include <iostream> using namespace std; void printarray (int arg[], int length) { for (int n=0; n<length; n++) cout << arg[n] << " "; cout << "\n"; } int main () { int firstarray[] = {5, 10, 15}; int secondarray[] = {2, 4, 6, 8, 10}; printarray (firstarray,3); printarray (secondarray,5); return 0; }

5 10 15 2 4 6 8 10

• char myword[] = { 'H', 'e', 'l', 'l', 'o', '\0' };

/ null-terminated sequences of characters#include <iostream>using namespace std;

int main (){ char question[] = "Please, enter your first name: "; char greeting[] = "Hello, "; char yourname [80]; cout << question; cin >> yourname; cout << greeting << yourname << "!"; return 0;}

declaring an initializing arrays:• Here are examples of declaring an initializing arrays:

• int number[12] = {18, 42, 25, 12, 34, 15, 63, 72, 92, 26, 26, 12};• double distance[5] = {44.14, 720.52, 96.08, 468.78, 6.28};• int number[] = {18, 42, 25, 12, 34, 15, 63, 72, 92, 26, 26, 12};• double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};

• int n, m; double x[5][6];• FILE *inp; inp = fopen("IN.DAT","r");• for (n = 0; n < 5; ++n) { for (m = 0; m < 6; ++m)

fscanf (inp, "%lf", &x[n][m]);• } fclose (inp);

//adding Matrix

#include<iostream.h>#include<conio.h>void main(){clrscr();int a[10][10],b[10][10],c[10][10],m,n,i,j;cout<<"Enter number of rows: ";cin>>m;cout<<"Enter number of coloumns: ";cin>>n;cout<<endl<<"Enter elements of matrix A: "<<endl;for(i=0;i<m;i++){for(j=0;j<n;j++){cout<<"Enter element a"<<i+1<<j+1<<": ";cin>>a[i][j];}}cout<<endl<<"Enter elements of matrix B: "<<endl;//Coding by: Snehil Khanor//http://WapCPP.blogspot.comfor(i=0;i<m;i++){for(j=0;j<n;j++){cout<<"Enter element b"<<i+1<<j+1<<": ";cin>>b[i][j];}}

Diagonal Matrix1 0 0 00 2 0 00 0 3 00 0 0 4

• x(i,j) is on diagonal iff i = j

• number of diagonal elements in an n x n matrix is n

• non diagonal elements are zero

• store diagonal only vs n2 whole

29

Program 7-2// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element short array to store the// values. #include <iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees: ";for (int count = 0; count < 6; count++)

cin >> hours[count];cout << "The hours you entered are:";for (count = 0; count < 6; count++)

cout << " " << hours[count];cout << endl;

}

30

Program 7-6// This program displays the number of days in each month.// It uses a 12-element int array.#include <iostream.h>

void main(void){

int days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};for (int count = 0; count < 12; count++){

cout << "Month " << (count + 1) << " has ";cout << days[count] << " days.\n";

}}

31

Program Output

Month 1 has 31 days.Month 2 has 28 days.Month 3 has 31 days.Month 4 has 30 days.Month 5 has 31 days.Month 6 has 30 days.Month 7 has 31 days.Month 8 has 31 days.Month 9 has 30 days.Month 10 has 31 days.Month 11 has 30 days.Month 12 has 31 days.


void MultiplyWithOutAMP() {

int aMatrix[3][2] = {{1, 4}, {2, 5}, {3, 6}}; int bMatrix[2][3] = {{7, 8, 9}, {10, 11, 12}}; int product[3][3] = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}}; for (int row = 0; row < 3; row++) { for (int col = 0; col < 3; col++) { // Multiply the row of A by the column of B to get the row, column of product. for (int inner = 0; inner < 2; inner++) { product[row][col] += aMatrix[row][inner] * bMatrix[inner][col]; } cout << product[row][col] << " "; } cout << "\n"; }

}

int main() { // cout << bMatrix[3][2] << "\t"; // cout << aMatrix[3][2] << "\t"; MultiplyWithOutAMP(); getchar();

system("pause"); return 0;}

Using pointer(Multiplier)#include <iomanip> #include <iostream>using namespace std;int main(){int **mat1;int **mat2;int **result;int row,col;cout<<"Please enter row/col"<<endl;cin>>row>>col;mat1 = new int *[row];mat2 = new int *[row];result = new int *[row];int k,i,j;for (k=0; i<row; k++) mat1[k] = new int[col]; mat2[k] = new int[col]; result[k] = new int[col]; for (i=0; i<row; i++) for (j=0; j<col; j++) for (j=0; j<row; j++) for(i=0; i<col; i++) result[i][k] += (mat1 [i][k] * mat2[k][j]);cout<<setw(4)<<result[i][k];

#include <iomanip> // pointer Multiplier #include <iostream>using namespace std;int main(){int **mat1;int **mat2;int **result;int row,col;cout<<"Please enter row/col"<<endl;cin>>row>>col;mat1 = new int *[row];mat2 = new int *[row];result = new int *[row];int k,i,j;for (k=0; k<row; k++) mat1[k] = new int[col]; mat2[k] = new int[col]; result[k] = new int[col]; for (i=0; i<row; i++) for (j=0; j<col; j++) mat1[k][i] = k + i; for (j=0; j<row; j++) mat2[i][k] = j + k; for(i=0; i<col; i++) result[i][k] += (mat1 [i][k] * mat2[k][j]);cout<<setw(4)<<result[i][k];

cout<<endl<<"Displaying Matrix A: "<<endl<<endl;for(i=0;i<m;i++){for(j=0;j<n;j++){cout<<a[i][j]<<" ";}cout<<endl<<endl;}cout<<endl<<"Displaying Matrix B: "<<endl<<endl;for(i=0;i<m;i++){for(j=0;j<n;j++){cout<<b[i][j]<<" ";}cout<<endl<<endl;}cout<<endl<<"Matrix A + Matrix B = Matrix C: "<<endl<<endl;for(i=0;i<m;i++){for(j=0;j<n;j++){cout<<a[i][j]+b[i][j]<<" ";}cout<<endl<<endl;}getch();}

Adding matrix: c++ program to add two matrices

#include<iostream> using namespace std; main(){ int m, n, c, d, first[10][10], second[10][10], sum[10][10]; cout << "Enter the number of rows and columns of matrix "; cin >> m >> n; cout << "Enter the elements of first matrix\n"; for ( c = 0 ; c < m ; c++ ) for ( d = 0 ; d < n ; d++ ) cin >> first[c][d]; cout << "Enter the elements of second matrix\n"; for ( c = 0 ; c < m ;c++ ) for ( d = 0 ; d < n ; d++ ) cin >> second[c][d]; for ( c = 0 ; c < m ; c++ ) for ( d = 0 ; d < n ; d++ ) sum[c][d] = first[c][d] + second[c][d]; cout << "Sum of entered matrices:-\n"; for ( c = 0 ; c < m ; c++ ) { for ( d = 0 ; d < n ; d++ ) cout << sum[c][d] << "\t"; cout << endl; } system("pause"); return 0;}

A number is taken from the user number with reverse digits is displayed

#include<iostream>using namespace std;int main(){//clrscr();long int n,rev=0,m;cout<<"please enter a five digit no.: ";cin>>n;while(n>0)//Coding by: Snehil Khanor//http://WapCPP.blogspot.com{m=n%10;rev=rev*10+m;n=n/10;}cout<<rev;//

system("pause"); return 0;}

Address in memory 1: #include <iostream> 2: 3: int main() 4: { 5: short age[4]; 6: age[0]=23; 7: age[1]=34; 8: age[2]=65; 9: age[3]=74; 10: 11: std::cout << age << std::endl; 12: return 0; 13: }

Character in Array 1: char letter[4]; 2: letter[0]='M'; 3: letter[1]='a'; 4: letter[2]='r'; 5: letter[3]='k'; 6: ... *(letter+2) ...

• Question (4)• • Using the switch or if statement, write a C program that takes in an

integer numerical grade num_grade from the keyboard and returns to the screen a letter_grade according to

• the following scale:• letter_grade is A if num_grade ≥ 90• letter_grade is B if 80 ≤ num_grade < 90• letter_grade is C if 70 ≤ num_grade < 80• letter_grade is D if 60 ≤ num_grade < 70• letter_grade is F if num_grade < 60• Check the correctness of your program and print down the outputs

of your program for a• student with a score of 100 and another with a score of 65.

include <iostream>using namespace std;

int main(){

double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};

cout << "2nd member = " << distance[1] << endl;cout << "5th member = " << distance[4] << endl;

return 0;}

This would produce:

2nd member = 720.525th member = 6.28


int main(){

double distance[] = {44.14, 720.52, 96.08, 468.78, 6.28};


return 0;}• This would produce:

• Distance 1: 44.14• Distance 2: 720.52• Distance 3: 96.08• Distance 4: 468.78• Distance 5: 6.28


int main(){



return 0; }


int main(){

// We know that we need a constant number of elementsconst int max = 10;int number[max];

// We will calculate their sumint sum = 0;

cout << "Please type 10 integers.\n";

for( int i = 0; i < max; i++ ){

cout << "Number " << i + 1 << ": ";cin >> number[i];sum += number[i];

}

cout << "\n\nThe sum of these numbers is " << Sum << "\n\n";

return 0;}


void DisplayTheArray(double member[5]);

int main(){


return 0;}

void DisplayTheArray(double member[5]){

for(int i = 0; i < 5; ++i)cout << "\nDistance " << i + 1 << ": " << member[i];

cout << endl;}

Declaring and Initializing a 2-Dimensional Array


int main(){

// A 2-Dimensional arraydouble distance[2][4] = {44.14, 720.52, 96.08, 468.78, 6.28, 68.04, 364.55, 6234.12};

// Scan the array from the 3rd to the 7th membercout << "Members of the array";cout << "\nDistance [0][0]" << ": " << distance[0][0];cout << "\nDistance [0][1]" << ": " << distance[0][1];cout << "\nDistance [0][2]" << ": " << distance[0][2];cout << "\nDistance [0][3]" << ": " << distance[0][3];cout << "\nDistance [1][0]" << ": " << distance[1][0];cout << "\nDistance [1][1]" << ": " << distance[1][1];cout << "\nDistance [1][2]" << ": " << distance[1][2];cout << "\nDistance [1][3]" << ": " << distance[1][3];


}

2-Dimensional array#include <iostream>using namespace std;

int main(){

// A 2-Dimensional arraydouble distance[][4] = {

{ 44.14, 720.52, 96.08, 468.78 },{ 6.28, 68.04, 364.55, 6234.12 }

};

// Scan the array from the 3rd to the 7th membercout << "Members of the array";for(int i = 0; i < 2; ++i)

for(int j = 0; j < 4; ++j)cout << "\nDistance [" << i << "][" << j << "]: " << distance[i][j];


}

Multidimensional Arrays

• #include <iostream>• using namespace std;

• void MultiplyWithOutAMP() {

• int aMatrix[3][2] = {{1, 4}, {2, 5}, {3, 6}};• int bMatrix[2][3] = {{7, 8, 9}, {10, 11, 12}};• int product[3][3] = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};

• for (int row = 0; row < 3; row++) {• for (int col = 0; col < 3; col++) {• // Multiply the row of A by the column of B to get the row, column of product.• for (int inner = 0; inner < 2; inner++) {• product[row][col] += aMatrix[row][inner] * bMatrix[inner][col];• }• std::cout << product[row][col] << " ";• }• std::cout << "\n";• }• }

• main() {• MultiplyWithOutAMP();• getchar();• system("pause");• }

#include <iostream>using namespace std;#define MAX 50

void mulmatvec(int m, int n, double a[MAX][MAX], double x[MAX], double b[MAX]){ int i,j;

for(i = 0; i < m; i++){ b[i] = 0.; for(j = 0; j < n; j++) b[i] += a[i][j]*x[j]; } return;}

int main(){ int i,j,m,n; double a[MAX][MAX], x[MAX], b[MAX];

cout << "Enter the number of rows in the matrix \n"; cin >> m; cout << "Enter the number of columns in the matrix \n"; cin >> n;

cout << "Enter the matrix by rows\n"; for(i = 0; i < m; i++) for(j = 0; j < n; j++) cin >> a[i][j];

cout << "Enter the vector\n"; for(j = 0; j < n; j++) cin >> x[j];

mulmatvec(m,n,a,x,b);

cout << "\nA*x = \n"; for(i = 0; i < m; i++) cout << b[i] << "\n";}

•#include<iostream>#include<conio.h>using namespace std;int main(){ int i,j; int arr[6][6]; for(i=0;i<=5;i++){ for(j=5;j>=0;j--){ if(i+j==5) arr[i][j]=0; 'diagonal else if(i+j>5) arr[i][j]=-1; 'lower-right side else arr[i][j]=1; 'upper-left side } } for(i=0;i<=5;i++){ for(j=0;j<=5;j++) cout<<arr[i][j]<<"\t"; cout<<endl; } getch(); return 0; }

• Initializing array• To assign values to the array, you can write those

values as below.• int i[]= {1, 2, 3, 4, 5};//The array got values

or• int i[5];• i[0]=1;• i[1]=2;• i[2]=3;• i[3]=4;• i[4]=5;

Adding two Matrix#include<iostream> using namespace std; main(){ int m, n, c, d, first[10][10], second[10][10], sum[10][10]; cout << "Enter the number of rows and columns of matrix "; cin >> m >> n; cout << "Enter the elements of first matrix\n"; for ( c = 0 ; c < m ; c++ ) for ( d = 0 ; d < n ; d++ ) cin >> first[c][d]; cout << "Enter the elements of second matrix\n"; for ( c = 0 ; c < m ;c++ ) for ( d = 0 ; d < n ; d++ ) cin >> second[c][d]; for ( c = 0 ; c < m ; c++ ) for ( d = 0 ; d < n ; d++ ) sum[c][d] = first[c][d] + second[c][d]; cout << "Sum of entered matrices:-\n"; for ( c = 0 ; c < m ; c++ ) { for ( d = 0 ; d < n ; d++ ) cout << sum[c][d] << "\t"; cout << endl; } return 0;}

Matrix multiplication in C++

• Matrices can be used to perform transformations. For example, in 2D and 3D space. Transformations include, but are not limited to, rotating, scaling and translating. Transformations can be combined by multiplying the matrices with each other.

• For example, you might want to:• scale an object with a factor of 2• rotate it 45 degrees around the Y-axis• translate it to (5,5,5)• Each of the above steps can be represented with a four by four

matrix (four rows and four columns). Multiplication of matrices is done by multiplying each row of the first matrix with each column of the second matrix and summing up the results. The number of columns of the first matrix needs to be equal to the number of rows of the second matrix. For example (4 x 4) x (4 x 4) is allowed. However, (4 x 3) x (4 x 3) is not allowed.

http://en.wikipedia.org/wiki/Matrix_(mathematics)

http://en.wikipedia.org/wiki/Transformation_matrix

http://en.wikipedia.org/wiki/Transformation_matrix#Rotation

http://en.wikipedia.org/wiki/Transformation_matrix#Scaling

http://en.wikipedia.org/wiki/Translation_(geometry)

Matrix multiplication

[[1x1 + 2x0 + 3x0 + 4x0] = 1, [1x0 + 2x1 + 3x0 + 4x0] = 2, [1x0 + 2x0 + 3x1 + 4x0] = 3, [1x0 + 2x0 + 3x0 + 4x1] = 4]]

Code #include <iostream>

void MultiplyWithOutAMP() {

int aMatrix[3][2] = {{1, 4}, {2, 5}, {3, 6}}; int bMatrix[2][3] = {{7, 8, 9}, {10, 11, 12}}; int product[3][3] = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};

for (int row = 0; row < 3; row++) { for (int col = 0; col < 3; col++) { // Multiply the row of A by the column of B to get the row, column of product. for (int inner = 0; inner < 2; inner++) { product[row][col] += aMatrix[row][inner] * bMatrix[inner][col]; } std::cout << product[row][col] << " "; } std::cout << "\n"; }}

void main() { MultiplyWithOutAMP(); getchar();}

// C++ multiplication of the matrix x and matrix y and stores the result in matrix z#include <iostream>using namespace std; #define m 3#define c 2#define n 4 int main(void){int i, j, k; // first matrixint x[m][c] = {{1,2},{3,4},{5,6}};// second matrixint y[c][n] = {{7,8,9,10},{11,12,13,14}};// for storing the matrix product resultint z[m][n]; for(i=0; i<m; i++)for(j=0; j<n; j++){z[i][j] = 0;for(k=0; k<c; k++)// same as z[i][j] = z[i][j] + x[i][k] * y[k][j];z[i][j] += x[i][k] * y[k][j];}cout<<"\nMultiply matrix x and matrix y,";cout<<"\nThen store the result in matrix z.";cout<<"\nMatrix x is 3x2, and matrix y is 2x4,";cout<<"\nso, the result, z should be matrix 3x4\n";cout<<"\nThe matrix product is: \n";for (i=0; i<m; i++){cout<<"\n";for(j=0; j<n; j++)// display the result...cout<<" "<<z[i][j];}cout<<endl; return 0;}

Output example: Multiply matrix x and matrix y,Then store the result in matrix z.Matrix x is 3x2, and matrix y is 2x4,so, the result, z should be matrix 3x4The matrix product is:29 32 35 3865 72 79 86101 112 123 134Press any key to continue . . .

67

Chapter 7 – Arrays

68

7.1 Arrays Hold Multiple values

• Unlike regular variables, arrays can hold multiple values.

69

Figure 7-1

int count Enough memory for 1 int

12345

float price Enough memory for 1 float

56.981

char letter Enough memory for 1 char

A

70

Figure 7-2

71

Table 7-1

Array Declaration Number of Elements

Size of Each Element

Size of the Array

char letters[25]; 25 1 byte 25 bytes short rings[100]; 100 2 bytes 200 bytes int miles[84]; 84 4 bytes 336 bytes float temp[12]; 12 4 bytes 48 bytes doubledDistance[1000]; 1000 8 bytes 8000 bytes

72

7.2 Accessing Array elements

• The individual elements of an array are assigned unique subscripts. These subscripts are used to access the elements.

73

Program 7-1// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element int array to store the// values.

#include <iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees: ";cin >> hours[0];cin >> hours[1];cin >> hours[2];cin >> hours[3];

74

Program continuescin >> hours[4];cin >> hours[5];cout << "The hours you entered are:";cout << " " << hours[0];cout << " " << hours[1];cout << " " << hours[2];cout << " " << hours[3];cout << " " << hours[4];cout << " " << hours[5] << endl;

}

75

Program Output with Example Input

Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter]

The hours you entered are: 20 12 40 30 30 15

76

Figure 7-7

77

Program 7-2// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element short array to store the// values. #include <iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees: ";for (int count = 0; count < 6; count++)

cin >> hours[count];cout << "The hours you entered are:";for (count = 0; count < 6; count++)

cout << " " << hours[count];cout << endl;

}

78


Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter]

The hours you entered are: 20 12 40 30 30 15

79

Program 7-3// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element short array to store the// values.#include<iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees.\n";for (int count = 1; count <= 6; count++){

cout << "Employee " << count << ": ";cin >> hours[count - 1];

}cout << "The hours you entered are\n";

80

Program continues

for (count = 1; count <= 6; count++){

cout << "Employee " << count << ": ";cout << hours[count - 1] << endl;

}

}

81


Enter the hours worked by six employees.Employee 1: 20 [Enter]Employee 2: 12 [Enter]Employee 3: 40 [Enter]Employee 4: 30 [Enter]Employee 5: 30 [Enter]Employee 6: 15 [Enter]The hours you entered areEmployee 1: 20Employee 2: 12Employee 3: 40Employee 4: 30Employee 5: 30Employee 6: 15

82

7.3 No Bounds Checking in C++

• C++ gives you the freedom to store data past an array’s boundaries.

83

Program 7-4// This program unsafely accesses an area of memory by writing// values beyond an array's boundary.// WARNING: If you compile and run this program, it could cause// the computer to crash.#include <iostream.h>

void main(void){

short values[3]; // An array of 3 short integers.

cout << "I will store 5 numbers in a 3 element array!\n";for (int count = 0; count < 5; count++)

values[count] = 100;cout << "If you see this message, it means the computer\n";cout << "has not crashed! Here are the numbers:\n";for (int count = 0; count < 5; count++)

cout << values[count] << endl;

}

84

Figure 7-8

85

7.4 Array Initialization

• Arrays may be initialized when they are declared.

86

Program 7-5

// This program displays the number of days in each month.// It uses a 12-element int array.


void main(void){

int days[12];days[0] = 31; // Januarydays[1] = 28; // Februarydays[2] = 31; // Marchdays[3] = 30; // Aprildays[4] = 31; // Maydays[5] = 30; // Junedays[6] = 31; // July

87

Program continues

days[7] = 31; // Augustdays[8] = 30; // Septemberdays[9] = 31; // Octoberdays[10] = 30; // Novemberdays[11] = 31; // Decemberfor (int count = 0; count < 12; count++){


}

}

88

Program Output


89

Program 7-6// This program displays the number of days in each month.// It uses a 12-element int array.#include <iostream.h>

void main(void){

int days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};for (int count = 0; count < 12; count++){


}}

90

Program Output


91

Program 7-7// This program uses an array of ten characters to store the// first ten letters of the alphabet. The ASCII codes of the// characters are displayed.#include <iostream.h>

void main(void){

char letters[10] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'};

cout << "Character" << "\t" << "ASCII Code\n";cout << "--------" << "\t" << "----------\n";for (int count = 0; count < 10; count++){

cout << letters[count] << "\t\t";cout << int(letters[count]) << endl;

}}

92

Program Output

Character ASCII Code--------- ----------

A 65B 66C 67D 68E 69F 70G 71H 72I 73

J 74

93

Partial Array Initialization

• When an array is being initialized, C++ does not require a value for every element.

int numbers[7] = {1, 2, 4, 8};

94

Program 7-8// This program has a partially initialized array.


void main(void){

int numbers[7] = {1, 2, 4, 8}; // Initialize the // first 4 elements.

cout << "Here are the contents of the array:\n";for (int index = 0; index < 7; index++)

cout << numbers[index] << endl;}

95

Program Output

Here are the contents of the array:1248000

96

Implicit Array Sizing

• It is possible to declare an array without specifying its size, as long as you provide an initialization list.

float ratings[] = {1.0, 1.5, 2.0, 2.5, 3.0};

97

Initializing With Strings

• When initializing a character array with a string, simply enclose the string in quotation marks:

char name[] = “Warren”;

98

Figure 7-11

99

Program 7-9// This program displays the contents of two char arrays.#include <iostream.h>

void main(void){

char name1[] = "Holly";char name2[] = {'W', 'a', 'r', 'r', 'e', 'n', '\0'};

cout << name1 << endl;cout << name2 << endl;

}

100

Program Output

HollyWarren

101

7.5 Processing Array Contents

• Individual array elements are processed like any other type of variable.

102

Program 7-10// This program stores, in an array, the hours worked by 5// employees who all make the same hourly wage.


void main(void){

int hours[5];float payRate;

cout << "Enter the hours worked by 5 employees who all\n";cout << "earn the same hourly rate.\n";for (int index = 0; index < 5; index++){

cout << "Employee #" << (index + 1) << ": ";cin >> hours[index];

}

103

Program continues

cout << "Enter the hourly pay rate for all the employees: ";cin >> payRate;cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){

float grossPay = hours[index] * payRate;cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}

104


Enter the hours worked by 5 employees who allearn the same hourly rate.Employee #1: 5 [Enter]Employee #2: 10 [Enter]Employee #3: 15 [Enter]Employee #4: 20 [Enter]Employee #5: 40 [Enter]Enter the hourly pay rate for all the employees: 12.75

[Enter]Here is the gross pay for each employee:Employee #1: $63.75Employee #2: $127.50Employee #3: $191.25Employee #4: $255.00Employee #5: $510.00

105

Program 7-11// This program stores, in an array, the hours worked by 5// employees who all make the same hourly wage. It then// displays the gross pay, including any overtime.


// Constant for defining the array size

void main(void){

int hours[5];float payRate;

cout << "Enter the hours worked by 5 employees who all\n";cout << "earn the same hourly rate.\n";for (int index = 0; index < 5; index++){

cout << "Employee #" << (index + 1) << ": ";cin >> hours[index];

}

106

Program continuescout << "Enter the hourly pay rate for all the employees: ";cin >> payRate;cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){

float grossPay, overTime;if (hours[index] > 40){

// Calculate pay for 40 hours.grossPay = 40 * payRate; // Calculate overtime pay.overTime = (hours[index] - 40) * 1.5 *

payRate;// Add regular pay and overtime pay.grossPay += overTime;

}

107

Program continues

elsegrossPay = hours[index] * payRate;

cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}

108


Enter the hours worked by 5 employees who allearn the same hourly rate.Employee #1: 10 [Enter]Employee #2: 20 [Enter]Employee #3: 50 [Enter]Employee #4: 40 [Enter]Employee #5: 60 [Enter]

Enter the hourly pay rate for all the employees: 12.75 [Enter]

Here is the gross pay for each employee:Employee #1: $127.50Employee #2: $255.00Employee #3: $701.25Employee #4: $510.00Employee #5: $892.50

109

7.6 Focus on Software Engineering: Parallel Arrays

• By using he same subscript, you can build relationships between data stored in two or more arrays.

110

Program 7-12// This program stores, in two arrays, the hours worked by 5// employees, and their hourly pay rates.#include <iostream.h>

// Constant for defining the array sizeconst int numEmps = 5;

void main(void){

int hours[numEmps];float payRate[numEmps];

cout << "Enter the hours worked by “ << numEmps << “ employees and their\n";

cout << "hourly rates.\n"; for (int index = 0; index < numEmps; index++){

cout << "hours worked by employee #" << (index + 1);cout << ": ";

111

Program continues

cin >> hours[index];cout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> payRate[index];

}cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < numEmps; index++){

float grossPay = hours[index] * payRate[index];cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}

112

Program Output with Example InputEnter the hours worked by 5 employees and their hourly

rates.hours worked by employee #1: 10 [Enter]Hourly pay rate for employee #1: 9.75 [Enter]hours worked by employee #2: 15 [Enter]Hourly pay rate for employee #2: 8.62 [Enter]hours worked by employee #3: 20 [Enter]Hourly pay rate for employee #3: 10.50 [Enter]hours worked by employee #4: 40 [Enter]Hourly pay rate for employee #4: 18.75 [Enter]hours worked by employee #5: 40 [Enter]Hourly pay rate for employee #5: 15.65 [Enter]

Here is the gross pay for each employee:Employee #1: $97.50Employee #2: $129.30Employee #3: $210.00

113

7.7 Thou Shalt Not Assign

• You cannot use the assignment operator to copy one array’s contents to another.

for (int count=0; count < 4; count++)

newVal[count] = oldVal[count];

114

Table 7-2

Expression Value

O ld V alues[0 ] 10 (Contents of Element 0 of O ld V alues)




N ew V alues 8012 (Memory Address of N ew V alues)

O ld V alues 8024 (Memory Address of O ld V alues)

115

7.8 Printing the Contents of an Array

• To display the contents of an array, you must use a loop to display the contents of each element.

int array[5] = { 10, 20, 30, 40, 50 };for (int count = 0; count < 5; count++)

cout << array[count] << endl;

116

7.9 Arrays As Function Arguments

• To pass an array as an argument to a function, pass the name of the array.

117

Program 7-13// This program demonstrates that an array element is passed// to a function like any other variable.#include <iostream.h>

void ShowValue(int); // Function prototype

void main(void){

int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40};

for (int Cycle = 0; Cycle < 8; Cycle++)ShowValue(collection[Cycle]);

}

118

Program continues

//************************************// Definition of function showValue. *// This function accepts an integer argument. *// The value of the argument is displayed. *//************************************void ShowValue(int Num){

cout << Num << " ";}

119

Program Output

5 10 15 20 25 30 35 40

120

Program 7-14// This program demonstrates an array being passed to a function.#include <iostream.h>

void showValues(int []); // Function prototype

void main(void){

int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40};

showValues(collection); // Passing address of array collection}

//***********************************************// Definition of function showValues. *// This function accepts an array of 8 integers *// as its argument. The contents of the array *// is displayed. *//***********************************************void showValues(int nums[]){

for (int index = 0; index < 8; index++)cout << nums[index] << " ";

}

121

Program Output

5 10 15 20 25 30 35 40

122

Program 7-15// This program demonstrates an array being passed to a function.#include <iostream.h>

void showValues(int []); // Function prototype

void main(void){

int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40};int set2[8] = {2, 4, 6, 8, 10, 12, 14, 16};showValues(set1);cout << endl;showValues(set2);

}

//***********************************************// Definition of function showValues. *// This function accepts an array of 8 integers *// as its argument. The contents of the array *// is displayed. *//***********************************************void showValues(int nums[]){

for (int index = 0; index < 8; index++)cout << nums[index] << " ";

}

123

Program Output

5 10 15 20 25 30 35 402 4 6 8 10 12 14 16

124

Program 7-16// This program uses a function that can display the contents// of an integer array of any size.#include <iostream.h>

void showValues(int [], int); // Function prototype

void main(void){

int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40};int set2[4] = {2, 4, 6, 8};int set3[12] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

showValues(set1, 8);cout << endl;showValues(set2, 4);cout << endl;showValues(set3, 12);

}

125

Program continues

//***********************************************// Definition of function showValues. *// This function displays the contents of the *// array passed into nums. The value passed *// into elements is the number of elements in *// the nums array. *//***********************************************

void showValues(int nums[], int elements){

for (int index = 0; index < elements; index++)cout << nums[index] << " ";

}

126

Program Output

5 10 15 20 25 30 35 402 4 6 81 2 3 4 5 6 7 8 9 10 11 12

127

Program 7-17// This program uses a function that doubles the contents of// the elements within an array.#include <iostream.h>

void doubleArray(int [], int); // Function prototypeconst int arraySize = 12;

void main(void){

int set[arraySize] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};cout << "The arrays values are:\n";for (int index = 0; index < arraySize; index++)

cout << set[index] << " ";cout << endl;doubleArray(set, arraySize);cout << "After calling doubleArray, the values are:\n";

128

Program continuesfor (int index = 0; index < arraySize; index++)

cout << set[index] << " ";cout << endl;

}

//**************************************************// Definition of function doubleArray. *// This function doubles the value of each element *// in the array passed into nums. *// The value passed into size is the number of *// elements in the nums array. *//**************************************************void doubleArray(int nums[], int size){

for (int index = 0; index < size; index++)nums[index] *= 2;

}

129

Program Output

The array values are:1 2 3 4 5 6 7 8 9 10 11 12After calling doubleArray, the values are:2 4 6 8 10 12 14 16 18 20 22 24

130

7.10 Two-dimensional Arrays

• A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data.

131

Program 7-18// This program demonstrates a two-dimensional array.


void main(void){

float sales[3][4]; // 2D array, 3 rows and 4 columns.float totalSales = 0; // To hold the total sales.int dir, qtr; // Loop counters.

132

Program continuescout << "This program will calculate the total sales of\n";cout << "all the company's divisions.\n";cout << "Enter the following sales information:\n\n";

// Nested loops to fill the array with quarterly// sales figures for each division.for (div = 0; div < 3; div++){

for (qtr = 0; qtr < 4; qtr++){

cout << "Division " << (div + 1);cout << ", Quarter " << (qtr + 1) << ": $";cin >> sales[div][qtr];

}cout << endl; // Print blank line.

}

133

Program continues

// Nested loops to add all the elements.for (div = 0; div < 3; div++)

for (qtr = 0; qtr < 4; qtr++)totalSales += sales[div][qtr];

cout.precision(2);cout.setf(ios::fixed | ios::showpoint);cout << "The total sales for the company are: $";cout << totalSales << endl;

}

134

Program Output with Example InputThis program will calculate the total sales ofall the company's divisions.Enter the following sales information:

Division 1, Quarter 1: $31569.45 [Enter]Division 1, Quarter 2: $29654.23 [Enter]Division 1, Quarter 3: $32982.54 [Enter]Division 1, Quarter 4: $39651.21 [Enter]


135

Output continues


The total sales for the company are: $456782.34

136

Passing Two-dimensional Arrays to Functions

• When a two-dimensional array is passed to a function, the parameter type must contain a size declarator for the number of columns.

137

7.11 Arrays of Strings

• A two-dimensional array of characters can be used as an array of C-strings.

138

Program 7-20// This program displays the number of days in each month.// It uses a two-dimensional character array to hold the // names of the months and an int array to hold the number// of days.#include <iostream.h>

void main(void){

char months[12][10] = {"January", "February", "March", "April", "May", "June",

"July", "August", "September”, "October", "November","December"};int days[12] = { 31, 28, 31, 30,

31, 30, 31, 31, 30, 31, 30, 31};

for (int count = 0; count < 12; count++){

cout << months[count] << " has ";cout << days[count] << " days.\n";

}}

139

Program 7-20 (continued)Program OutputJanuary has 31 days.February has 28 days.March has 31 days.April has 30 days. May has 31 days. June has 30 days. July has 31 days.August has 31 days. September has 30 days. October has 31 days. November has 30 days.December has 31 days.

140

Three Dimensional Arrays and Beyond

• C++ allows you to create arrays with virtually any number of dimensions.

• Here is an example of a three-dimensional array declaration:

float seat[3][5][8];

141

7.14 Introduction to the STL vector

• The Standard Template Library (or STL) is a collection of data types and algorithms that you may use in your programs. These data types and algorithms are programmer-defined. They are not part of the C++ language, but were created in addition to the built-in data types.

142


• The data types that are defined in the STL are commonly called containers, because they store and organize data.

• There are two types of containers in the STL: sequence containers and associative containers.

• The vector data type is a sequence container.

143


• A vector is like an array in the following ways:– A vector holds a sequence of values, or

elements.– A vector stores its elements in contiguous

memory locations.– You can use the array subscript operator [] to

read the individual elements in the vector

144


• However, a vector offers several advantages over arrays. Here are just a few:– You do not have to declare the number of

elements that the vector will have. – If you add a value to a vector that is already full,

the vector will automatically increase its size to accommodate the new value.

– vectors can report the number of elements they contain.

145

Declaring a vector

• To use vectors in your program, you must first #include the vector header file with the following statement:

#include <vector>

Note: There is no .h at the end of the file name.

146

Declaring a vector

• The next step is to include the following statement after your #include statements:

using namespace std;

The STL uses namespaces to organize the names of its data types and algorithms.

147

Declaring a vector

• Now you are ready to declare an actual vector object. Here is an example:

vector<int> numbers;

The statement above declares numbers as a vector of ints.

148

Declaring a vector

• You can declare a starting size, if you prefer. Here is an example:

vector<int> numbers(10);

The statement above declares numbers as a vector of 10 ints.

149

Other examples of vector Declarations

Declaration Format Description

vector<float> amounts; Declares amounts as an empty vector of floats.

vector<int> scores(15); Declares scores as a vector of 15 ints.

vector<char> letters(25, 'A'); Declares letters as a vector of 25 characters. Each element is initialized with 'A'.

vector<double> values2(values1); Declares values2 as a vector of doubles. All the elements of values1, which also a vector of doubles, are copied to value2.

150

Storing and Retrieving Values in a vector

• To store a value in an element that already exists in a vector, you may use the array subscript operator [].

151

Program 7-23// This program stores, in two vectors, the hours worked by 5// employees, and their hourly pay rates.#include <iostream.h>#include <vector> // Needed to declare vectorsusing namespace std;

void main(void){

vector<int> hours(5); // Declare a vector of 5 integersvector<float> payRate(5); // Declare a vector of 5 floats

cout << "Enter the hours worked by 5 employees and their\n";cout << "hourly rates.\n";for (int index = 0; index < 5; index++){

cout << "Hours worked by employee #" << (index + 1);cout << ": ";cin >> hours[index];cout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> payRate[index];

}

152

Program 7-23 (continued)cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){ float grossPay = hours[index] * payRate[index];

cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}

153

Program 7-23 (continued)Program Output with Example Input Shown in Bold

Enter the hours worked by 5 employees and theirhourly rates.Hours worked by employee #1: 10 [Enter]Hourly pay rate for employee #1: 9.75 [Enter]Hours worked by employee #2: 15 [Enter]Hourly pay rate for employee #2: 8.62 [Enter]Hours worked by employee #3: 20 [Enter]Hourly pay rate for employee #3: 10.50 [Enter]Hours worked by employee #4: 40 [Enter]Hourly pay rate for employee #4: 18.75 [Enter]Hours worked by employee #5: 40 [Enter]Hourly pay rate for employee #5: 15.65 [Enter]Here is the gross pay for each employee:Employee #1: $97.50Employee #2: $129.30Employee #3: $210.00Employee #4: $750.00Employee #5: $626.00

154

Using the push_back Member Function

• You cannot use the [] operator to access a vector element that does not exist.

• To store a value in a vector that does not have a starting size, or is already full, use the push_back member function. Here is an example:

numbers.push_back(25);

155

Program 7-24// This program stores, in two vectors, the hours worked by a specified// number of employees, and their hourly pay rates.

#include <iostream.h>#include <vector> // Needed to declare vectorsusing namespace std;

void main(void){

vector<int> hours; // hours is an empty vectorvector<float> payRate; // payRate is an empty vectorint numEmployees; // The number of employees

cout << "How many employees do you have? ";cin >> numEmployees;cout << "Enter the hours worked by " << numEmployees;cout << " employees and their hourly rates.\n";

156

Program 7-24 (continued)for (int index = 0; index < numEmployees; index++){

int tempHours; // To hold the number of hours enteredfloat tempRate; // To hold the payrate entered

cout << "Hours worked by employee #" << (index + 1);cout << ": ";cin >> tempHours;hours.push_back(tempHours); // Add an element to hourscout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> tempRate;payRate.push_back(tempRate); // Add an element to payRate

}cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < numEmployees; index++){

float grossPay = hours[index] * payRate[index];cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}

157


How many employees do you have? 3 [Enter] Enter the hours worked by 3 employees and their hourly rates.Hours worked by employee #1: 40 [Enter]Hourly pay rate for employee #1: 12.63 [Enter]Hours worked by employee #2: 25 [Enter]Hourly pay rate for employee #2: 10.35 [Enter]Hours worked by employee #3: 45 [Enter]Hourly pay rate for employee #3: 22.65 [Enter]Here is the gross pay for each employee:Employee #1: $505.20Employee #2: $258.75Employee #3: $1019.25

158

Determining the Size of a vector

• Unlike arrays, vectors can report the number of elements they contain. This is accomplished with the size member function. Here is an example of a statement that uses the size member function:

numValues = set.size();

• In the statement above, assume that numValues is an int, and set is a vector. After the statement executes, numValues will contain the number of elements in the vector set.

159

Determining the Size of a vector

• Example:

void showValues(vector<int> vect){

for (int count = 0; count < vect.size(); count++)cout << vect[count] << endl;

}

160

Program 7-25// This program demonstrates the vector size // member function.#include <iostream.h>

#include <vector>using namespace std; // Function prototypevoid showValues(vector<int>); void main(void){

vector<int> values;

for (int count = 0; count < 7; count++)values.push_back(count * 2);

showValues(values);}

161

Program 7-25 (continued)//**************************************************// Definition of function showValues. *// This function accepts an int vector as its *// argument. The value of each of the vector's *// elements is displayed. *//************************************************** void showValues(vector<int> vect){

for (int count = 0; count < vect.size(); count++)cout << vect[count] << endl;

}

162

Program 7-25 (continued)

Program Output 024681012

163

Removing Elements from a vector

• Use the pop_back member function to remove the last element from a vector.

collection.pop_back(); The statement above removes the last element from the collection vector.

164

Program 7-26// This program demosntrates the vector size member function. #include <iostream.h>#include <vector>using namespace std; void main(void){

vector<int> values;

// Store values in the vectorvalues.push_back(1);values.push_back(2);values.push_back(3);cout << "The size of values is " << values.size() << endl;

// Remove a value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;

165

Program 7-26 (continued)// Now remove another value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;

// Remove the last value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;

}

Program Output

The size of values is 3Popping a value from the vector...The size of values is now 2Popping a value from the vector...The size of values is now 1Popping a value from the vector...The size of values is now 0

166

Clearing a vector

• To completely clear the contents of a vector, use the clear member function. Here is an example:

numbers.clear(); After the statement above executes, the numbers vector will be cleared of all its elements.

167

Program 7-27// This program demosntrates the vector size member function.#include <iostream.h>#include <vector>using namespace std; void main(void){

vector<int> values(100);

cout << "The values vector has “<< values.size() << " elements.\n";

cout << "I will call the clear member function...\n";values.clear();cout << "Now, the values vector has “

<< values.size() << " elements.\n";}

168

Program 7-27 (continued)

Program Output The values vector has 100 elements.I will call the clear member function...Now, the values vector has 0 elements.

169

Detecting an Empty vector

• To determine if a vector is empty, use the empty member function. The function returns true if the vector is empty, and false if the vector has elements stored in it. Here is an example of its use:

if (set.empty())cout << "No values in set.\n";

170

Program 7-28// This program demosntrates the vector's empty member function. #include <iostream.h>#include <vector>using namespace std; // Function prototypefloat avgVector(vector<int>); void main(void){

vector<int> values;int numValues;float average;

cout << "How many values do you wish to average? ";cin >> numValues;

171

Program 7-28 (continued)for (int count = 0; count < numValues; count++){

int tempValue;

cout << "Enter a value: ";cin >> tempValue;values.push_back(tempValue);

}average = avgVector(values);cout << "Average: " << average << endl;

} //*************************************************************// Definition of function avgVector. *// This function accepts an int vector as its argument. If *// the vector contains values, the function returns the *// average of those values. Otherwise, an error message is *// displayed and the function returns 0.0. *//*************************************************************

172

Program 7-28 (continued)float avgVector(vector<int> vect){

int total = 0; // accumulatorfloat avg; // average

if (vect.empty()) // Determine if the vector is empty{

cout << "No values to average.\n";avg = 0.0;

}else{

for (int count = 0; count < vect.size(); count++)total += vect[count];

avg = total / vect.size();}return avg;

}

173


How many values do you wish to average?Enter a value: 12Enter a value: 18Enter a value: 3Enter a value: 7Enter a value: 9Average: 9 Program Output with Example Input Shown in Bold

How many values do you wish to average? 0No values to average.Average: 0

174

Summary of vector Member Functions

Member Function Description

at(element) Returns the value of the element located at element in the vector. Example:x = vect.at(5);The statement above assigns the value of the 5 th element of vect to x.

capacity() Returns the maximum number of elements that may be stored in the vector without additional memory being allocated. (This is not the same value as returned by the size member function).Example:x = vect.capacity();The statement above assigns the capacity of vect to x.

175


clear() Clears a vector of all its elements.Example:vect.clear();The statement above removes all the elements from vect.

empty() Returns true if the vector is empty. Otherwise, it returns false.Example:if (vect.empty()) cout << "The vector is empty.";The statement above displays the message if vect is empty.

pop_back() Removes the last element from the vector.Example:vect.pop_back();The statement above removes the last element of vect, thus reducing its size by 1.

176


push_back(value) Stores a value in the last element of the vector. If the vector is full or empty, a new element is created.Example:vect.push_back(7);The statement above stores 7 in the last element of vect.

reverse() Reverses the order of the elements in the vector (the last element becomes the first element, and the first element becomes the last element.)Example:vect.reverse();The statement above reverses the order of the element in vect.

resize(elements, value)

Resizes a vector by elements elements. Each of the new elements is initialized with the value in value.Example:vect.resize(5, 1);The statement above increases the size of vect by 5 elements. The 5 new elements are initialized to the value 1.

177


swap(vector2) Swaps the contents of the vector with the contents of vector2.Example:vect1.swap(vect2);The statement above swaps the contents of vect1 and vect2.

Date post:	17-Jan-2016
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GE 211 Programming in C++ Array &Matrix Dr. Ahmed Telba.

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