Why i am getting sum as output even i am not returning the value?

Question

sum(int a,int b)
{
    int x;
    x = a+b;
}
int main()
{ 
    printf("%d",sum(2,3));
}

If i remove the x then it will return first parameter always, but I am not returning any value.

Because [undefined behavior](https://stackoverflow.com/q/32132574/10077). — Fred Larson, Jun 06 '18 at 15:38
Upped as this question is nicely written with a compilable example. Remember, C gives you the ability to shoot yourself in the foot. That's why you need to follow the rules. And please use a compiler that will puke if a function doesn't have an explicit return type: that's been banned since C99. — Bathsheba, Jun 06 '18 at 15:40
@PetarVelev: Ahem! I have Microsoft Excel down as the best application ever written. — Bathsheba, Jun 06 '18 at 15:43
@Bathsheba Then you most likely haven't seen much programs really — Edenia, Jun 06 '18 at 15:44
@Edenia: I've seen enough. Sadly this ain't the site, but I can't resist. Care to state a couple of programs that you consider better? — Bathsheba, Jun 06 '18 at 15:45
@Bathsheba Gladly: notepad, windows itself and this: http://i46.tinypic.com/293hj6w.jpg — Edenia, Jun 06 '18 at 15:47
@Bathsheba Probably yes for its purpose. I had a different point there. — Petar Velev, Jun 06 '18 at 15:47

Sourav Ghosh · Answer 1 · 2018-06-06T15:47:10.110

1

You are trying to make use of a function call return value and the function does not have a return statement in it.

Directly quoting C11, chapter §6.9.1 (for functions other than main(), ^Footnote)

If the } that terminates a function is reached, and the value of the function call is used by the caller, the behavior is undefined.

Footnote:

From chapter §5.1.2.2.3

[...] reaching the } that terminates the main function returns a value of 0.

edited Jun 06 '18 at 15:47

answered Jun 06 '18 at 15:44

Sourav Ghosh

133,132
16
183
261

Other than main(). – Bathsheba Jun 06 '18 at 15:45
@Bathsheba true indeed, but recursive call to main is not a very good idea, either, :) – Sourav Ghosh Jun 06 '18 at 15:46
Worth adding to the answer though to make it correct? Note that calling main from itself is UB in C++. – Bathsheba Jun 06 '18 at 15:46
@Bathsheba there you go. :) – Sourav Ghosh Jun 06 '18 at 15:48
1

@Bathsheba you gotta teach me the trick to the no-printing characters, please. :) – Sourav Ghosh Jun 06 '18 at 16:30

score -1 · Answer 2 · answered Jun 06 '18 at 15:40

int sum(int a,int b)
 {
     int x;
     x = a+b;
     return x;
 }
 int main()
 { 
     printf("%d",sum(2,3));
 }`

this is how your code should look, you're getting results sometimes as x is a local variable and its value persists on the stack until it's overwritten, so you may end up getting the value you want, or you may end up getting some garbage

Why i am getting sum as output even i am not returning the value?

2 Answers2