How Can I Convert Float to Int with Modulus in C?

Question

I am so confused with Modulus in C. I am writing a small script that allows the user to input their two number vars, then they can either add, subtract, multiply, divide (easy) or modulus (haven't caught this one yet). What would I be doing wrong in this? I get the "invalid operands to binary %" error, which means I need to format it to an int since it is a float. However what is the best way of doing this with the following? Any C help would be greatly appreciated.

int main (void)
{
    float number1, number2, result;
    char symbol;

    //allow user interaction
    printf("Enter your formula: \n");
    scanf("%f %c %f", &number1, &symbol, &number2);



    switch (symbol) {
     case '%':
      result = number1 % number2;
      printf("Result: %f \n", result);
      break;
     default:
      printf("Operation Error. Program aborted. \n \n");
      break;
    }

    printf("Press any key to continue \n");

    getchar();
    return 0;
}

Where and how do I convert this?

Answer 1

Mod is an integer operation, so it cannot be used on floats. Your case should read something like:

result = (int)number1 % (int)number2;

which will convert both floats to integers, and perform the mod. However, note that you are losing precision by casting a floating point number to an integer, so it is likely the result may not be what you'd expect.

Answer 2

I recommend to use the fmod function of the standard C library.

Answer 3

change

case '%':
     result = number1 % number2;

to

case '%':
    result = (int)number1 % (int)number2;

?

modulo division is for integers. Cast each operand to an integer.

Answer 4

You can either use a statement like:

result = (int)number1 % (int)number2;

to cast your floats to ints and perform the modulus operation, but you'll lose the decimal precision.

You could also include math.h and use fmod

result = fmod(number1, number2);

Answer 5

The % operator only works on integer types. To perform the same task with floating points, you'd want to do something like:

#include <math.h>
float modulus(float a, float b)
{
   return a - b * floor(a / b);
}