// Demonstration of everyday binary search.
// No input.  Output is result from searching for each number in -1..24
#include <stdio.h>

int a[10]={0,2,4,6,8,10,12,14,16,18};

int binSearch(int *a,int n,int key)
// Input: int array a[] with n elements in ascending order.
//        int key to find.
// Output: Returns some subscript of a where key is found.
//         Returns -1 if not found.
// Processing: Binary search.
{
  int low,high,mid;
  low=0;
  high=n-1;
// subscripts between low and high are in search range.
// size of range halves in each iteration.
  while (low<=high)
  {
    mid=(low+high)/2;
    if (a[mid]==key)
      return mid; // key found
    if (a[mid]<key)
      low=mid+1;
    else
      high=mid-1;
  }

  return (-1); // key does not appear
}

int main()
{
int i;

for (i=(-1);i<25;i++)
  printf("key==%d returned %d\n",i,binSearch(a,10,i));
}