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I am trying to overload the % operator in C++ to make it do division instead of modulo. For example, 5 % 4 should give me 1.25 after overloading.

But I get "nan". Why?

This is the code I tried (but I get nan as the answer):

#include <iostream>
using namespace std;

class Modulo {
   public:
   int x;
   Modulo(int a) {
       x = a;
   }

   float operator%(const Modulo& other) {
       float result = float(x / (float)other.x);
   }
};

int main()
{
    Modulo m1(5), m2(4);
    cout <<  m1%m2;
}
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7
  • 10
    Your operator doesn't return anything. Please enable warnings on your compiler. Commented Aug 2 at 19:55
  • 3
    @Robert I agree except the problem is like a typo in the code, and better close it for that Commented Aug 2 at 20:10
  • 1
    What people mean by enable warnings, you will then get something like this : godbolt.org/z/5zfdzhvWz Commented Aug 2 at 20:15
  • 4
    @bruno -- "overload" is correct. Yes, the definition inside the class defines an operator, but the choice of which version of the operator to use depends on the types of the arguments, and that's overloading. 5 % 4 still calculates the remainder of integer division. Commented Aug 2 at 20:56
  • 5
    An aside: why would you want to overload the modulo operator to behave like division?? Mathematically, although there is a relationship between modulo and division, they are different operators because they have different effects. Commented Aug 2 at 22:57

1 Answer 1

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4

Don't you get a warning or two when you compile your code? If not, you should really crank up the warning level. On gcc, it's -Wall for starters. This question has some background and details on C and C++ warnings.

The compiler tells you what's wrong:

robert:~$ gcc modulo.cpp
modulo.cpp: In member function ‘float Modulo::operator%(const Modulo&)’:
modulo.cpp:15:5: warning: no return statement in function returning non-void [-Wreturn-type]

You calculate result, but never do anything with it. With -Wall you'd also get a warning about the unused variable. Bottom line: there is no return value, and still you try to print it. At best you get nan, for me it just crashes and burns.

Add return result; to float operator%(const Modulo& other):

float operator%(const Modulo& other) {
    float result = float(x / (float) other.x);
    return result;
}

Besides that, don't use this code in real life: it's very confusing to redefine the modulo operator to do division. There's a / operator for that. You'll confuse the heck out of yourself and your peers. Unrelated, but also important: get in the habit of consistently indenting your code. It makes it much easier to read. And enable all compiler warnings.

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