010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

C Language Part 3C Language Part 3

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Arrays

An array is a data structure containing a certain number of elements, all of which have the same type To declare an array, specify the type and number of the elementsFor example, int a[10]; declares a to be an array of 10 integers

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Arrays (contd.)

To access an element of an array, write the array name followed by a subscriptIn C, subscripts always start with 0 For example, the elements of array a are a[0], a[1], … , a[9]

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Arrays (contd.)

An array is initialized by listing the valuesIf the number of values is less than that of the array elements, the remaining elements are given value 0

int a[10] = {9, 8, 7, 6, 5, 4, 3, 2, 1, 0};

int a[10] = {0};

float a[3] = { 0.1, 0.2, 0.0 };

int a[3] = { 3, 4 };

int a[] = { 2, -4, 1 };

int a[4] = { 2, -4, 1 };

char s[] = “abcd”;

char s[] = { ‘a’,‘b’,‘c’,‘d’,‘\0’ }

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Finding MaximumThe program below reads ten values into an array ab and then finds the maximum among the values#include <stdio.h>

int main(void){ int n, i, max; int ab[10];  printf("Enter n: "); scanf("%d", &n); printf("Enter n numbers: "); for (i=0; i<n; i++) scanf("%d", &ab[i]);  max = ab[0]; for (i=1; i<n; i++) if (ab[i] > max) max = ab[i]; printf("max %d\n", max); return 0;}

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Bubble SortSorts array ab of n elements in non-decreasing orderThe first iteration of the inner for loop brings the maximum element to the last position, the second iteration brings the second maximum to the second-to-last position, etc.The three assignments inside the if statement exchange the values of ab[j] and ab[j+1]

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Bubble Sort (contd.)

for (i=1; i<n; i++)for (j=0; j<n-i; j++)

if (ab[j] > ab[j+1]) {temp = ab[j];ab[j] = ab[j+1];ab[j+1] = temp;

}

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

void insertionSort( int a[], int n )

{

int i, j, val;

for( i = 1; i < n; i++){

val = a[i];

j = i - 1;

while ( ( j >= 0 ) && ( a[j] > val ) ) {

a[j+1] = a[j];

j--;

}

a[j+1] = val;

printIntArray( a, n );

}

}

Insertion Sort

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

#include <stdio.h>

#define N 10

void insertionSort( int *, int );

void printIntArray( int *, int );

int main( void )

{

int a[N] = { 23, -3, 5, 9, 11,

33, 87, -7, -24, 50 };

printIntArray( a, N );

insertionSort( a, N );

return 0;

}

void printIntArray( int a[], int n ){ int i;

for( i = 0; i < n; i++) printf("%4d ", a[i]);

printf("\n");}

Insertion Sort (contd.)

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

23 -3 5 9 11 33 87 -7 -24 50

-3 23 5 9 11 33 87 -7 -24 50

-3 5 23 9 11 33 87 -7 -24 50

-3 5 9 23 11 33 87 -7 -24 50

-3 5 9 11 23 33 87 -7 -24 50

-3 5 9 11 23 33 87 -7 -24 50

-3 5 9 11 23 33 87 -7 -24 50

-7 -3 5 9 11 23 33 87 -24 50

-24 -7 -3 5 9 11 23 33 87 50

-24 -7 -3 5 9 11 23 33 50 87

Insertion Sort (contd.)

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Search

Suppose that n elements are stored in an array abGiven a new element x, we want to find if x is in array ab

x is one of the elements stored in ab

An easy solution for search is to scan the elements in array ab one by one and check if it is equal to x

Linear search

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Linear Search#include <stdio.h>int main(void){ int n, i, x; int ab[100];  printf("Enter n: "); scanf("%d", &n); printf("Enter n numbers: "); for (i=0; i<n; i++)

scanf("%d", &ab[i]); printf("Enter x: ");

scanf("%d", &x); for (i=0; i<n; i++)

if (x == ab[i]) { printf("%d\n", i); return 0; }

printf("%d\n", -1); return -1;}

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Binary SearchIf the elements in array ab are stored in non-decreasing order after sorting, we can solve the search problem more efficiently than linear searchWe first compare x with the element in the middle (i.e., median)

If x is equal to the median, we have found it

If x is smaller than the median, we are sure that x is not in the upper part of array ab, so we look for x in the lower part

Otherwise, x is larger than the median, we look for x in the upper part

Binary search is faster than linear search

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Binary Search (contd.)

low = 0;high = n-1;while (low <= high) {

mid = (low+high) / 2; if (x < ab[mid])

high = mid – 1; else if (x > ab[mid])

low = mid + 1; else {

printf("%d\n", mid); return 0;

}}printf("%d\n", -1);return -1;

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Two-dimensional Arrays

Two dimensional arrays can be visualized as a multicolumn table or gridint b[2][5];

Declares a two-dimensional array b that has 2 rows and 5 columns

We can initialize a two-dimensional array as follows:

int b[2][5] = {{1,0,0,1,1},{0,0,1,1,1}};

010.133 Digital Computer Concept and PracticeCopyright ©2012 by Jaejin Lee

Math.hThe library <math.h> contains mathematical functions (x is of type double, and all functions return double)sqrt(x) square root of xexp(x) exponential function exlog(x) natural logarithm ln(x)log10(x) log10(x)sin(x) sine of xcos(x) cosine of xtan(x) tangent of x