C Program for Binary Search (Recursive and Iterative)

We basically ignore half of the elements just after one comparison.

  1. Compare x with the middle element.
  2. If x matches with middle element, we return the mid index.
  3. Else If x is greater than the mid element, then x can only lie in right half subarray after the mid element. So we recur for right half.
  4. Else (x is smaller) recur for the left half.

Recursive :

C/C++

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#include <stdio.h>
  
// A recursive binary search function. It returns location of x in
// given array arr[l..r] is present, otherwise -1
int binarySearch(int arr[], int l, int r, int x)
{
   if (r >= l)
   {
        int mid = l + (r - l)/2;
  
        // If the element is present at the middle itself
        if (arr[mid] == x)  return mid;
  
        // If element is smaller than mid, then it can only be present
        // in left subarray
        if (arr[mid] > x) return binarySearch(arr, l, mid-1, x);
  
        // Else the element can only be present in right subarray
        return binarySearch(arr, mid+1, r, x);
   }
  
   // We reach here when element is not present in array
   return -1;
}
  
int main(void)
{
   int arr[] = {2, 3, 4, 10, 40};
   int n = sizeof(arr)/ sizeof(arr[0]);
   int x = 10;
   int result = binarySearch(arr, 0, n-1, x);
   (result == -1)? printf("Element is not present in array")
                 : printf("Element is present at index %d", result);
   return 0;
}

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Iterative

C/C++

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#include <stdio.h>
  
// A iterative binary search function. It returns location of x in
// given array arr[l..r] if present, otherwise -1
int binarySearch(int arr[], int l, int r, int x)
{
  while (l <= r)
  {
    int m = l + (r-l)/2;
  
    // Check if x is present at mid
    if (arr[m] == x) 
        return m;  
  
    // If x greater, ignore left half  
    if (arr[m] < x) 
        l = m + 1; 
  
    // If x is smaller, ignore right half 
    else 
         r = m - 1; 
  }
  
  // if we reach here, then element was not present
  return -1; 
}
  
int main(void)
{
   int arr[] = {2, 3, 4, 10, 40};
   int n = sizeof(arr)/ sizeof(arr[0]);
   int x = 10;
   int result = binarySearch(arr, 0, n-1, x);
   (result == -1)? printf("Element is not present in array")
                 : printf("Element is present at index %d", result);
   return 0;
}

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Please refer complete article on Binary Search for more details!

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