C Program for Binary Search

                Binary Search is applicable only when the array is sorted. This method makes a comparison between the ‘key’ (element to be searched) and middle element of array.

                Since elements are sorted, comparisons may result in either a match or comp could be continued with either left or right half of element. Left half element can be selected by making ub=mid-1. Right half element, can be selected by making ub=mid+1. The process of selecting either left half or right half continues until the element is found or element is not there.

                Ex.

                                               

• Consider array of size N having element as shown, make variable lb=0, and ub=n-1=5-1=4.
• Read number of to be searched, N=44
• Find mid= (lb+ub)/2=2

• Compare, if a[mid]==N number but 44 is greater than 30, Hence make lb=mid+1=3.

• Find mid=(lb+ub)/2=(3+4)/2=3           a[mid]=a[3]=44

• Compare, if (a[mid]==N)            44==44

Hence number is found in two comparison which is at 4th position, print it on screen.

Program:-

#include <stdio.h>

int main(void)

{

int i,key,a[12],n,flag=0;

int lb=0,mid,ub;

printf("\n how many element in array");

scanf("\n%d",&n);

ub=n-1;

printf("\n enter array element\n");

for(i=0;i<n;i++)

{

scanf("\n%d",&a[i]);

}

printf("\n enter the number to be search=");

scanf("\n%d",&key);

mid=(lb+ub)/2;

while(lb<=ub)

{

if(a[mid]==key)

{

flag=1;

break;

}

else if(key<mid)

ub=mid-1;

else

lb=mid+1;

mid=(lb+ub)/2;

}

if(flag==0)

printf("\n Number is not found");

else

printf("\n%d Number is found at location %d",key,mid+1);

return 0;

}

Output:-

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