C :

#include<stdio.h>
int a[100010];
int fac(int p,int q,int x)
{   int z;z=0;

	z=p+(q-p)/2;

 if(p>q)
  {printf("-1");return 0;
	 }
	if(x==a[z])
     {printf("%d",z);return 1;
	 }
   	else
	{
	
		if(x>a[z]) fac(z+1,q,x);
	
	
		else  fac(p,z-1,x);
		
		
		
		
	}
	
	
	
	
	
	
}
int main()
{
	int n,x,i;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	{ 
		scanf("%d",&a[i]);

		
	}
	
		scanf("%d",&x);
	
fac(1,n,x);
	
}

C++ :

#include<iostream>
using namespace std;
const int max1=1000000;
int a[max1],n,m;
int  flag;
int search(int ,int, int );
int main()
{  
	cin>>n;
	for (int i=1; i<=n; ++i) cin>>a[i];
	cin>>m;
	flag=search(1,n,m);
	//if (flag) cout<<"YES"<<endl;
	//	else  cout<<"NO"<<endl;
	cout<<flag<<endl;
	return 0;
}
int  search(int l,int r,int m)
{
	int mid=(l+r)/2;
	if (l>r) return -1;
		else if (a[mid]==m) return mid;	
			else if (a[mid]>m) 
				return search(l,mid-1,m);
			else return search(mid+1,r,m);
}

Pascal :

program binary_find;
type arr=array[1..100005] of longint;
function bf_dg(l,r,x:longint;a:arr):longint;
var m:longint;
begin
  if l>r then exit(-1);
  m:=(l+r) div 2;
  if x=a[m] then exit(m);
  if x<a[m] then exit(bf_dg(l,m-1,x,a))
  else
    exit(bf_dg(m+1,r,x,a));
end;
function bf(n,x:longint;a:arr):longint;
var l,r,m:longint;
begin
  l:=1; r:=n;
  while l<=r do
  begin
    m:=(l+r) div 2;
    if x=a[m] then exit(m);
    if x<a[m] then r:=m-1
    else l:=m+1;
  end;
  exit(-1);
end;

var
  a:arr;
  n,x,i:longint;
begin
  readln(n);
  for i:=1 to n do read(a[i]);
  readln(x);
  writeln(bf(n,x,a));
  readln;
end.