#include <stdio.h>                    
#include <unistd.h>                   
#include <string.h>                   

int good(int addr) {
        printf("Address of hmm: %p\n", addr);
}                                            

int hmm() {
        printf("Win.\n");
        execl("/bin/sh", "sh", NULL);
}                                    

extern char **environ;

int main(int argc, char **argv) {

        int i, limit;

        for(i = 0; environ[i] != NULL; i++)
        memset(environ[i], 0x00, strlen(environ[i]));

        int (*fptr)(int) = good;
        char buf[32];

        if(strlen(argv[1]) <= 40) limit = strlen(argv[1]);

        for(i = 0; i <= limit; i++) {
                buf[i] = argv[1][i];
                if(i < 36) buf[i] = 0x41;
        }

        int (*hmmptr)(int) = hmm;

        (*fptr)((int)hmmptr);

        return 0;

}

I don't really understand the code above, i have it from an online game - i should supply something in the arguments so it would give me shell, but i don't get it how it works so i don't know what to do. So i need someone that would explain it what it does, how it's working and the stuff. Thanks.