void

hello everyone!
i found a strange thing.
1.i inputed the codes followed in "CodeBlocks",but it returned this "error:'main' must return 'int'".why?

Code:

#include<stdio.h>
void main()
{
    printf("hello world!");
}

2.but it run smoothly,when writing in this way(just without "void"):

Code:

#include<stdio.h>
 main()
{
    printf("hello world!");
}

3.the two case all can run smoothly in "TC".

why?

i find the reason in thispage.

say thanks to laserlight,tabstop,adak,nkrao@gmail haha

in wich compiler u getting that error? i mean in "TC" or "GCC" ?

Because "TC" doesn't believe in standards. The standard for the C language requires that main return int. (The C standard allows you, but discourages you, to declare a function without a return type and have it default to int.)

Originally Posted by luoyangke

1.i inputed the codes followed in "CodeBlocks",but it returned this "error:'main' must return 'int'".why?

Because according to the C standard (or at least its intended interpretation, for a hosted environment like the one you are using, the main function must be defined with a return type of int.

Originally Posted by luoyangke

2.but it run smoothly,when writing in this way(just without "void"):

When the return type is not specified, it defaults to int. However, you should not rely on this. (Unfortunately, I was not able to quickly determine if the feature is obsolescent or simply not recommended).

Originally Posted by nkrao123@gmail.

in wich compiler u getting that error? i mean in "TC" or "GCC" ?

a thing named "CodeBlocks" thank you!

Originally Posted by tabstop

Because "TC" doesn't believe in standards. The standard for the C language requires that main return int. (The C standard allows you, but discourages you, to declare a function without a return type and have it default to int.)

thank you ! but i still don't understand

Turbo C assumes all functions without a return type, return an int, even though you did not specify a return at all.

Conversely, if you did specify a return type, then it will expect you also to specify the return explicitly, at the end of that function. If the function has a return type of void, then it will give you an error if you specify a return type.

so,

Code:

main() { //int return is assumed and handled by the compiler - OK

}

int main() { //int is specified and return is, as well - OK

  return 0;
}

but 
int main() { //int return type specified, but not present. Causes a compiler error

}

Originally Posted by laserlight

Because according to the C standard (or at least its intended interpretation, for a hosted environment like the one you are using, the main function must be defined with a return type of int.


When the return type is not specified, it defaults to int. However, you should not rely on this. (Unfortunately, I was not able to quickly determine if the feature is obsolescent or simply not recommended).

thank you! not just for this answer 谢谢！

Originally Posted by Adak

Turbo C assumes all functions without a return type, return an int, even though you did not specify a return at all.

Conversely, if you did specify a return type, then it will expect you also to specify the return explicitly, at the end of that function. If the function has a return type of void, then it will give you an error if you specify a return type.

so,

Code:

main() { //int return is assumed and handled by the compiler - OK

}

int main() { //int is specified and return is, as well - OK

  return 0;
}

but 
int main() { //int return type specified, but not present. Causes a compiler error

}

thanks for the second time

Originally Posted by Adak

Code:

int main() { //int return type specified, but not present. Causes a compiler error

}

However, third version as quoted above is equivalent to the second version according to the 1999 edition of the C standard (which Turbo C presumably does not support).

Originally Posted by luoyangke

thank you! not just for this answer

You're welcome