How to test whether a number is perfect square ?

How to test whether a number is perfect square ?

use binary search to check whether the number is perfect square

bool foo(int low,int high,int num)
{
 if(low>high)
  return false;
 int mid=(low+high)/2;
 if(mid*mid==num)
  return true;
 if(mid*mid<num)
  return foo(mid+1,high,num);
 return foo(low,mid-1,num);

}

note the perfect square has odd factors