Program for finding square root of number

Question

So I wrote a program to find floor of square of a number. It seems to work fine for smaller numbers but for long numbers it gives weird results. Here is my code.

int SquareRoot(long x)
{
  long start=1;
  long end=x;
  long mid;

  while(start<end)
  {
     mid=start+(end-start+1)/2;
     if(mid*mid<x)
     {
        if((mid+1)*(mid+1)>x)
        {
            return mid;
        }
       start=mid;
     }
     else if(mid*mid>x)
     {

         if((mid-1)*(mid-1<x)
            return mid-1;
        end=mid;
    }
    else
        return mid;
  }
  return start;
}

Answer 1

Probably the "weird results" you observe happen when one or both of the computations mid * mid and (mid + 1) * (mid + 1) overflows, which will happen when end is bigger than 2*sqrt(LONG_MAX) (approximately 6,074,000,998 if long is 64 bits, or 92680 if long is 32 bits).

The overflow will cause the comparison with x to produce an erroneous result (technically, the overflow produces Undefined Behaviour although with gcc the result is predictable but incorrect).