Questions about C Function Prototypes and Compilation

Question

With the following code:

int main(){
    printf(\"%f\\n\",multiply(2));
    return 0;
}

float multiply(float n){
    return n * 2;
}

When

Answer 1

An unspecified function has a return type of int (that's why you get the warning, the compiler thinks it returns an integer) and an unknown number of unspecified arguments.

If you break up your project in multiple files, just declare a function prototype before you call the functions from the other files, and all will work fine.