Thread: Very basic C question

I'm totally new at C (I've only done some Java and PHP earlier), so this is a very basic question.

Why doesn't the following work?

Code:

main() {
        float fl1, fl2;
        fl1 = 2.5;
        fl2 = 2.5;
        printf("%f\n", addition2(fl1,fl2));
        //printf("%f\n", fl1+fl2);
}

float addition2(float fl1, float fl2) {
        return fl1+fl2;
}

The commented out printf line works fine, but when I call a method that returns the same calculation it fails with this compilation error (in gcc):

test.c: In function ‘main’:
test.c:7: warning: format ‘%f’ expects type ‘double’, but argument 2 has type ‘int’
test.c: At top level:
test.c:11: error: conflicting types for ‘addition2’
test.c:7: error: previous implicit declaration of ‘addition2’ was here

I don't understand the line "argument 2 has type 'int'"...

If I change all float variables, in main and the addition() method, and the placeholders to int data types, it works fine. So there's apparently a trick to doing this with float variables which I haven't learned.

Ah, thank you very kindly Sir.

That should've been obvious to me, really. How about creating a funtion prototype of an int method too? It's not necessary, but maybe it makes the code more tidy?

Originally Posted by cnewbie1

Ah, thank you very kindly Sir.

That should've been obvious to me, really. How about creating a funtion prototype of an int method too? It's not necessary, but maybe it makes the code more tidy?

If you mean something like this:

Code:

#include <stdio.h>

float addition2(float fl1, float fl2);
int addition2(int i1, int i2);

main() {
		//blablablah
}

float addition2(float fl1, float fl2) {
        return fl1+fl2;
}

int addition2(int i1, int i2){
		return i1 = i2;
}

This is called "function overloading" and is NOT allowed in C (but it is allowed in C++)

No, I was thinking of this:

Code:

#include <stdio.h>

int add(int, int);
float snitt(float, float, float);

main () {
     blah-blah;
}

int add(int x, int y) {
     return x+y;
}

float snitt(float v, float w, float z) {
     return (v+w+z)/3;
}

That is, use a function prototype for the int method appearing after main also, even though it's not necessary. It makes no difference, but I thought maybe it was more tidy. Or maybe not. Kind of the same way as it's tidy to declare all variables before initializing/using them.

Thanks for the help, tips and answers. Hopefully I can move on a bit now :-)