C :

#include<stdio.h>
int binary_search(int arr[], int n, int k)
{
   int i=-1;
   int low=0,high=n-1,mid;
   while(low<=high)
   {
     mid=(high+low)/2;
     if(arr[mid]==k)
     {
        i=mid;
        break;
     }
     else if(arr[mid]>k)
        high=mid-1;
     else
      low=mid+1;
  }
  return i;
} 
int main(){
	int n;
	scanf("%d",&n);
	int a[n];
	for(int i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	int key;
	scanf("%d",&key);
	int result = binary_search(a,n,key);
	if(result>=0){
			printf("%d",result+1);
			printf("\n"); 
	} 
	else{
		printf("-1");
	}
	return 0;
} 

C++ :

#include <iostream>
using namespace std;

//二分查找 
int binary(int a[],int n,int x){
	int r = -1;
	
	int left = 0;
	int right = n - 1;
	int mid;
	
	while(left <= right){
		mid = (left + right) / 2;
		if(a[mid] == x){
			r = mid;
			break;
		}else if(x < a[mid]){
			right = mid - 1;
		}else if(x > a[mid]){
			left = mid + 1;
		}
	}
	
	return r;
}

int main(){
	int n,i,x,p;
	int a[1000];
	cin>>n;
	for(i = 0;i < n;i++){
		cin>>a[i];
	}
	
	cin>>x;
	p = binary(a,n,x);
	if(p != -1){
		cout<<p + 1<<endl;	
	}else{
		cout<<p<<endl;
	}
	
	
}

Python :

n=int(input())
sr=input().split()
a=[]
for i in range(n):
    a.append(int(sr[i]))
x=int(input())
l=0
r=n-1
while(l<=r):
    m=(l+r)//2
    if(a[m]==x):
        print(m+1)
        break
    elif(a[m]>x):
        r=m-1
    else:
        l=m+1
if(l>r):
    print(-1)