Thread: No compiler/runtime error?

This is definitely a newbie question. I've got a very simple example where I expected to get a compile or runtime error, but it actually works, albeit with the wrong answer:

Code:

#include <stdio.h>
int square(int x) {
    return x*x;
}
int main() {
    float a = 12.5;
    int b = square(a);
    printf("%f^2 = %d\n", a, b);
    return 0;
}

If I compile it and run it, I get the following:

Code:

12.500000^2 = 144

It's the wrong answer and the wrong data type for the function call, but the C compiler allows it. Can someone point me to a reason?

Many thanks!

Originally Posted by lkr1919

It's the wrong answer and the wrong data type for the function call, but the C compiler allows it. Can someone point me to a reason?

It is called implicit type conversion, and the float 12.5 is automatically converted into the intefer, 12.

C is a weakly typed language (or, to paraphrase Peter van der Linden, C programmers think "strong typing" means hitting the keyboard harder). Arithmetic types (which is to say integers and floating point values) can be freely converted between each other, and the compiler is not required to complain. Note that this includes char, which is an integer. With a cast, C allows pointers and integers to be converted between each other, as well.

What this means is, be careful with types. You've seen the conversion between floating point an integral types, but there can also be issues when converting between signed and unsigned integral types, for example. The free conversion of types can be useful, but it is a double-edged sword.

That makes sense. Many thanks!