Why do I get the “invalid operands to binary expression” error?

Question

While trying to solve credit, I get the following error

rem and number1 are declared as long and even if I change them to int, I still get the same error.

Please provide a solution and explain what the mistake is!

Answer 1

The remainder operator (otherwise known as the modulo operator) % is a binary operator (i.e., takes exactly 2 operands) and operates only on integer types (e.g., short, int, long, long long, etc).

It appears from the error message that the variable number1 is of type double. Also, the function pow from the math library returns a value of type double. These two values are the main cause for the error.

There are many solutions to this each of which depend on what you want to do. I'll demonstrate a couple of them:

1. Casting the operands to ints

   foo = (int) bar % (int) quux; // WARNING: you'll be risking to lose data
   

2. Declaring number1 to be of an int type and writing your own version of pow that maybe takes and returns ints

   // works only for non-negative integer exponents
   int myPow(int n, int exp)
   {
       int result = 1;
       for (; exp > 0; exp--)
           result *= n;
   
       return result;
   }
   
   // some code
   
   foo = number1 % pow(bar, quux);
   

3. Declaring number1 to be of an int type and using a library function like round, to round the value returned from pow then casting it to an int

   foo = number1 % (int) round(pow(bar, quux));