/tmp>cat evil.c
#include <stdio.h>
#include <stdlib.h>

typedef int (*func_returning_int)(void);

typedef void (*func_returning_void)(void);

void dummy(void)
{
        puts("Hello World");
}

int main(int argc, char ** argv)
{
        func_returning_void f = &dummy;
        int i = 0;

        f();

        i = ((func_returning_int)f)();

        printf("i=%i\n",i);
        return 0;
}

/tmp>CFLAGS="-Wall -pedantic" make evil
cc -Wall -pedantic    evil.c   -o evil

/tmp>./evil
Hello World
Hello World
i=12

/tmp>