Binary Searching: Find first occurrence of element in sorted array

Binary searching is an algorithm to search an element in sorted array. Here is C program to find first occurrence of an element in array.

For example if array is {12,12,14,15,15,15,16,16,19,22} then first occurrence of element 12 is at index 0, first occurrence of element 15 is at index 3.

C Program:

#include<stdio.h>
int BSFOcurrence(int arr[],int size, int num)
{
	int low=0, high=size-1, mid;
	/* Initialize a variable to find first occurrence to 
	size of array. */
	int first_oc = size;
 
	while(low<=high)
	{
		mid = (low+high)/2;
 
 
		if(arr[mid]==num)
		{
			if(mid<first_oc)
			first_oc = mid;
			high = mid-1;
		}
		else
		if(arr[mid]<num)
		low = mid+1;
		else
		high = mid-1;
 
	}
	return first_oc;
}
int main()
{
	int arr[]={12,13,16,16,19,22,22,25,28};
 
	int size = sizeof(arr)/sizeof(arr[0]);
 
	int num;
 
	printf("Enter number ");
	scanf("%d",&num);
 
	int index = BSFOcurrence(arr,size,num);
 
	if(index == size)
	{
		printf("Number is not in array\n");
	}
	else
	{
		printf("First occurrence at index = %d",index);
	}
 
	return 0;
}