how return keyword work in main function or any user defined function?

Question

what basis that does function return 0 or 1 o especially in main()? is it possible that -1 is the return value?

Answer 1

By placing void in front of any function definition, you make it so that the function does not need to return a value. For example:

void test(void)
{
    ...
}

Would not return anything.