how to use custom functions in easyc pro

If I create a source file and create a function, such as

#include "Main.h"
int something() { return 5; }

inside of a Source File, how can I access this function inside the main block diagram? Is that possible?

By the way, I went to the Main blog diagram and added a code block that was simply


But when I compiled it said “Warning[2058] Main.c line# 5: call of function without prototype.”

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