int main(void) vs main()

Question

I am reading The C Programming Language and the first program is to print Hello World I wrote the code as it shown in the book:

#include <stdio.h>

main()
{
    printf("hello, world\n");
}

But I got an error warning: type specifier missing, defaults to 'int' [-Wimplicit-int] main(). I fixed it by writing the code like this:

#include <stdio.h>

int main()
{
    printf("hello, world\n");
}

Can anyone tell me what is the difference and why should I write it like that?

C++ clan is at war with the C clan. The fragile truce is maintained by keeping the C++ and C tags separated. — Ron, Oct 07 '17 at 18:31
@Ron I was always wandering why my bedroom looks like after a serious fight. Now I know - as I use both I have to have al least two personalities and they fight when I sleep. — 0___________, Oct 07 '17 at 18:47
@melpomene both were asked so many times - it is even not worth to comment - OP did not even use the google — 0___________, Oct 07 '17 at 18:48
@melpomene I't about the valid signature of `main` it's an exact duplicate — bolov, Oct 07 '17 at 19:10
@bolov incorrect. `main()` with implicit `int` still returns `int`, and takes no arguments. — Antti Haapala -- Слава Україні, Oct 07 '17 at 19:14
@AnttiHaapala there is an answer on the dupe dealing exactly with that: https://stackoverflow.com/a/31263079/2805305 — bolov, Oct 07 '17 at 19:28

score 0 · Answer 1 · answered Oct 07 '17 at 18:36

Older versions of C had the concept of a default type. If a variable is declared without a type, it is assumed to be int. Similarly with functions, if a function is defined without a return type, it is also assumed to return int.

More recent versions of C (i.e. versions less than 25 years old) did away with default types and output a warning in this case. It's best to explicitly specify the type to avoid ambiguity and keep with more modern C.

`Older versions of C` you shuld use the term _ancient_ instead — 0___________, Oct 07 '17 at 18:50

int main(void) vs main()

1 Answers1