main() function defined without return type gives warning

Question

This is my program:

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

I get this warning when compiling it:

function should retur         


        

Answer 1

c automatically implies the datatype int to functions with no declared datatype. So as far as the compiler is concerned the above is:

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

This expects that you would return an integer at the end of it with a return statement. If you explicitly specify it as void main() you are telling the compiler that the function does not have a return value, hence no warning.

The reason that this is not an error is that if not specified, main() will return 0; at the end of execution. However the compiler is still giving you a warning that this is happening.

Best practice is to use int main() and then return 0 at the end of your program execution like this.

int main()
{ 
    printf("hello world\n");
    return 0;
}

See: this question for more information.