Week 9, 10

Arrays (one-dimensional and two-

dimensional)

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ONE-DIMENSIONAL ARRAYS

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Arrays An array is like a large data variable that can store multiple data items of

the same type. Arrays are a series of elements (variables) of the same type placed

consecutively in memory that can be individually referenced by addingan index to a unique name.

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X

X[0]

Each individual

element is referred to by

the array name and the

subscript (or index).

Index starts with 0 and ends

with is the size-1;

The ith element is referred to by X[i-1]

Arrays We can store 5 values of type int without having to declare 5 different

variables each one with a different identifier. Instead of that, using anarray we can store 5 different values of the same type, int for example,with an unique identifier.

Example: Use an array called Arr to contain 5 integer values of type int.

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Arr0 1 2 3 4

int

The cells are numbered from 0 to 4 since in arrays the first index is

always 0, independently of its length .

Declaration of Array variables A typical array declaration in C is as follows:

type name [elements]; Example:

int X[10]; //

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Array X will contain 10 elements of integer type. The elements will be X[0] to X[9]

We can have arrays of any type and dimension:

Example: char X[20]

float Y[50]

double Z[10] NOTE: The elements field within brackets [] when declaringan array must be a constant value, since arrays are blocks ofstatic memory of a given size and the compiler must be able todetermine exactly how much memory must assign to the arraybefore any instruction is considered.

Initialising Arrays (1)

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When declaring an array of local scope (within a function), if we

do not specify otherwise, it will not be initialized. So, its content is

undetermined until we store some values in it.

If we declare a global array (outside any function) its contents will

be initialized with all its elements filled with zeros. Thus, if in the

global scope we declare int billy [5] :

0 0 0 0 0billy0 1 2 3 4

int But additionally, when we declare an Array, we have the possibility to assign initialvalues to each one of its elements using curly brackets { }.Example:int billy [5] = { 16, 2, 77, 40, 12071 };

Initialising Arrays (2)

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The number of elements in the array that we initialized within

curly brackets { } must match the length in elements that we

declared for the array enclosed within square brackets [ ].

Example: int array1 [5] = { 16, 2, 77, 40, 12071};

Because this can be considered an useless repetition, C++ includes

the possibility of leaving empty the brackets [ ], being the size of the

Array defined by the number of values included between curly

brackets { }:

Example: int array2 [] = { 16, 2, 77, 40, 12071};

Input/Output of array elements (1) Exercise: Write a program to input values into all elements of an

integer array A of size 10 and display back the values.

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#include

int main()

{

int A[10];

int i;

printf("Enter 10 integer values: ");

for (i=0; i

Input/Output of array elements (2) Exercise: Write a program to input values into all elements of an

integer array A of size 10 and display back the values in reverseorder.

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Solution#include int main(){

int A[10];int i;printf("Enter 10 integer values: ");for (i=0;i

Input/Output of array elements (3)

Exercise: Write a program to input an integer n (n

Solution

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#include

int main()

{

int i;

float A[10];

int maxposn;

float max;

printf("Input 10 integer numbers:

", n);

maxposn=0;

max=0;

for (i=0;imax)

{

max=A[i];

maxposn=i;

}

}

printf("largest is %.2f at posn

%d\n", max, maxposn);

}

Array of characters (1)

Character arrays can be treated in a similar way to arrays of integers and real numbers.

Example: char x[20] Each element can be input as follows:

for (i=0; i

Arrays of characters (2)

With the declaration char x[20], the arrayx can contain a string of characters. But a string contains \0 as the last character Reading a string:

char x[20];scanf("%s",x);After reading the characters (must be less than 20), a \0 will be

appended at the end.NOTE: It will stop input when a space is encountered or end of line is

encountered.

Displaying the value of x:printf(%s,x);

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Exercise - Write a program to input the name of a personand display the number of vowels in the name.

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Solution#include int main(){

char name[20];char ch;int i,count;count = 0;printf("Input name: ");scanf("%s", name);

i=0;while ((name[i]!='\0') && (i

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Strings/Array of characters (2)

Initialization of strings:

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

The above example shows a string of characters (array) of 6

elements of type char initialized with the characters that compose

Hello plus a null character '\0'.

Nevertheless, string of characters have an additional way to

initialize its values: using constant strings:

Example:

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

char mystring [] = "Hello";

In both cases the Array or string of characters mystring is

declared with a size of 6 characters (elements of type char): the 5

characters that compose Hello plus a final null character ('\0')

which specifies the end of the string. However, in the second case,

when using double quotes ("), the null character it is

automatically appended.

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Strings/Array of characters (3)

Note:

We can "assign" a multiple constant to an Array only at the

moment of initializing it, that is, at the moment it is being

declared.

The following examples are invalid:

astring = "Hello";

astring[] = "Hello";

astring = { 'H', 'e', 'l', 'l', 'o', '\0' };

However, the following is valid:

char astring[10] ;

astring[0] = 'H';

astring[1] = 'e';

astring[2] = 'l';

astring[3] = 'l';

astring[4] = 'o';

astring[5] = '\0;

Strings/Array of characters (4): string.h#include

can be used to access string manipulation functions e.g char name[]=John, x[5]; Useful functions are:

strlenInt L;L=strlen(name);

strcpystrcpy(x,name);

strcmpif(strcmp(name,x)==0)

printf(same\n);else

printf(not same\n);

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Strings/Array of characters (5): string.h#include #include int main(){

char name1[20], name2[20], tmp[20];

int i,L1,L2;

printf("Input name1: ");scanf("%s",name1);L1=strlen(name1);

printf("Input name2: ");scanf("%s",name2);L2=strlen(name2);

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printf("name1=%s, length is %d\n", name1,L1);

printf("name2=%s, length is %d\n", name2,L2);

strcpy(tmp,name1);

printf("tmp=%s, length is %d\n",

name1,strlen(tmp));

if(strcmp(name1,tmp)==0)

printf("same\n");

else

printf("not same\n");

return 1;

}

Arrays as Parameters to functions (1)

Arrays can also be parameters to functions

The following should however be noted: The dimension of the array should not be included

in the function declaration and the prototype When a whole array is a parameter it always

behaves as a reference parameter. Example: void procedure (int arg[])

Example: int myarray [40];A typical function call for where this array is being passed as parameter is:

procedure (myarray);

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Arrays as Parameters to functions (2)

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// Example of using arrays as parameters#include void printarray (int arg[], int length);int main (){

int firstarray[] = {5, 10, 15};int secondarray[] = {2, 4, 6, 8, 10};printarray (firstarray,3);printarray (secondarray,5);return 0;

}

void printarray (int arg[], int length){int n;for (n=0; n

TWO-DIMENSIONAL ARRAYS

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Two-Dimensional Arrays (1)

Two dimensional arrays can be used tomanipulate tables, and are defined asfollows: [dimesion1][dimension2];

Exampleint a[3][4];

We have defined a table with 3 rows and 4columns

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Two-dimensional arrays (2)

The elements of a may be shown as a table, as followsa[0][0] a[0][1] a[0][2] a[0][3]a[1][0] a[1][1] a[1][2] a[1][3]a[2][0] a[2][1] a[2][2] a[2][3]

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Two-dimensional arrays (3) - Rows

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a[0][0] a[0][1] a[0][2] a[0][3] row 0a[1][0] a[1][1] a[1][2] a[1][3] row 1a[2][0] a[2][1] a[2][2] a[2][3] row 2

Two-dimensional arrays (4) - Columns

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a[0][0] a[0][1] a[0][2] a[0][3]a[1][0] a[1][1] a[1][2] a[1][3]a[2][0] a[2][1] a[2][2] a[2][3]

column 0 column 1 column 2 column 3

Two-dimensional arrays (5) - Example

Considerint M[5][3];

Inputting values in array table:for(row=0;row

Two-Dimensional Arrays (2)

Outputting values of array table:for (x=0; x

Two-dimensional arrays as parameters to functions (1)

When we pass a two dimensional array asa parameter to a function, the value of thefirst dimension is ignored(as for one-dimensional arrays) but the value of thesecond dimension has to be specified

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Two-dimensional arrays as parameters to functions (2)

void printarray (int arg[][3], int rows){

int x, y;for (x=0; x

Two-dimensional arrays as parameters to functions (3) A program calling a function that takes as parameter a two-dimensional array

#include void printarray (int arg[][3], int rows);int main (){

int M[5][3];int row,col;for(row=0;row

Arrays An additional note

Since arrays are always passed asreference parameters to functions, We can write functions to input values in an

array

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Arrays A simple program with functions to input and

output elements in one-dimensional arrays#include void inputarray(int arg[], int length);void printarray (int arg[], int length);int main (){

int firstarray[3];int secondarray[5];

printf("Input details for firstarray\n");inputarray(firstarray,3);

printf("Input details for secondarary\n");inputarray(secondarray,5);

printf("firstarray contains: ");printarray (firstarray,3);

printf("secondarray contains: ");printarray (secondarray,5);return 0;

}

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void inputarray(int arg[], int length){

int i;printf("\tInput %d values: ", length);for(i=0;i

Arrays A simple program with functions to input and

output elements in a two-dimensional array#include void inputarray(int arg[][3], int rows);oid printarray (int arg[][3], int rows);int main (){

int M[5][3];

inputarray(M,5);printarray(M,5);return 1;

}

void inputarray(int arg[][3], int rows){

int row,col;for(row=0;row

Class Exercise Write a program that declares a 2-

dimensional array to store marks for 15students, in 6 modules for each student. Theprogram also declares a 1-dimensional arrayto store average marks (in 6 modules) for 15students.

Make use of functions: To input marks of 15 students in six modules To output marks of 15 students in six modules To output average marks of students

In the function main(), calculate the averagemarks and store in corresponding array.

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void input(float M[][6], int num){

int row,col;for(row=0;row

void output(float M[][6], int num){

int row,col;for(row=0;row

void output_average(float A[], int num){

int x;for(x=0;x

# include

void input(float M[][6], int num);void output(float M[][6], int num);void output_average(float A[], intnum);

int main(){

float Marks[15][6];float Avg[15];int x,y;float sum;

input(Marks,15);output(Marks,15);

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for(x=0;x