2 files 1 project

If I make 2 files in 1 project, and I execute it, but I want to execute only 1 file how do I do it?
I made a project with 2 files in it, 1 is int main() and 1 is int submain() now how do I execute the submain file? only int main() executes and I get to errors pls help.

You must have a function called int main.
If you you only compile and link one file, then both files needs int main.

Code:

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void main(void){  // ;)
  submain();
  }

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Global variables will be constructed before main() executes, but other than that only the runtime environment can execute something before main().

Code:

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struct foo
{
    foo ( ) { submain(); }
} runbefore;

int main()
{
}

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Most of the time something like this is not appropriate.