find num in array by binary method

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#include<iostream>
using namespace std;
void main()
{
const int size=8;
int num[size];
for(int i=0;i<size;i++)
     cin>>num[i];
cout<<"add number for finding in an array using binary method "<<endl;
int n;
cin>>n;
int lower=0,higher=size-1;
int a=size-1;
int index=lower+higher/2;
while(num[index]!=n&&index!=a)             //lower<=higher
{
a=index;
if(num[index]>n)
higher=index-1;
else
lower=lower+1;
index=lower+higher/2;
}
if(index==a)                               //lower>higher
cout<<"number you entered is wrong "<<endl;
else
cout<<"number is placed at ["<<index<<"] index"<<endl;
}