c++ - Testing if given number is integer

Question

I am trying to implement user defined function which tests if a number is an integer:

#include <iostream>
#include <typeinfo>
using namespace std;
bool   integer(float k){
                  if (k==20000) return false;;
                  if (k==(-20000)) return  false;
 if (k==0)  return true;
   if (k<0)  return integer(k+1);
   else if(k>0)  return integer (k-1);
   return false;
}
int main(){

    float s=23.34;
       float s1=45;
       cout<<boolalpha;
       cout<<integer(s)<<endl;
       cout<<integer(s1)<<endl;
       return 0;

}

So the idea is that,if a number is an integer, does not matter if it is a negative or positive , if we decrease or increase it by one, we must get zero, but the problem is, that how can we create upper and lower bounds for increasing and decreasing?

Answer 1

#include <cmath>

bool is_integer(float k)
{
  return std::floor(k) == k;
}

This solution should work for all possible values of k. I am pretty sure this is a case where you can safely compare floats using ==.

Try to thoughtfully name functions. integer does not give any clue what it actually does, so I changed the function name to something more meaningful.

For the future, testing if a number is integer should feel like a very simple operation, so you should have a strong feeling that the best solution will be very simple. I hope you realize your original solution is absurd for many reasons (biggest reason: it will cause a stack overflow for the vast majority of cases).