[C/C++] Small tip - Argument passed to main() function.

In general, main function is used as below.

int main(int argc, const char *argv[]) {

}

But, it can be expanded like below

int main(int argc, const char *argv[], const char **envp) {

        while (*envp) {

                printf("%s\n", *envp++);

        }

}

By this way, we can use environment variables easily.

=> This matches parameters of execle() and execvpe() at Linux.