Binary Search

ALGORITHM BinarySearch(A[0..n - 1], K)

//Implements nonrecursive binary search
//Input: An arrayA[0..n - 1] sorted in ascending order and
// a search key K

//Output: An index of the array’s element that is equal to K or -1 if there is //no such element

l ← 0; 
r ← n - 1

while l ≤ r do

m ← (l + r)/2

if K = A[m] 
return m

else if K < A[m] 
r ← m - 1

else l ← m + 1return -1  

C program:

#include <stdio.h>

int main()
{
   int c, first, last, middle, n, search, array[100];

   printf("Enter the number of elements\n");
   scanf("%d",&n);

   printf("Enter %d integers\n", n);

   for (c = 0; c < n; c++)
      scanf("%d",&array[c]);

   printf("Enter the value to find\n");
   scanf("%d", &search);

   first = 0;
   last = n - 1;
   middle = (first+last)/2;

   while (first <= last) {
      if (array[middle] < search)
         first = middle + 1;
      else if (array[middle] == search) {
         printf("%d found at location %d.\n", search, middle+1);
         break;
      }
      else
         last = middle - 1;

      middle = (first + last)/2;
   }
   if (first > last)
      printf("Not found! %d isn't present in the list.\n", search);

   return 0;
}

Output:
Enter the number of elements
5
Enter 5 integers
1
2
3
45
6
Enter the value to find
3
3 found at location 3.