Can’t use modulus on doubles?

I have a program in C++ (compiled using g++). I’m trying to apply two doubles as operands to the modulus function, but I get the following error:

error: invalid operands of types ‘double’ and ‘double’ to binary ‘operator%’

Here’s the code:

int main() {
    double x = 6.3;
    double y = 2;
    double z = x % y;
}