Tricky C program question concerning software security

While the software security exam is coming, I try to review some of the facultative homework. Just post one that seems impossible to figure out for me. May some “Da Niu” try to give a solution when seeing this by chance. The code has been modified a little in caseā€¦ but without changing the original intention.

#include <stdio.h>
#include <stdlib.h>

void foo(char s[]){
int main(){
    char S[1];
    printf("\nsomething shows up after exit");

The question is to find an input in order that the program will print “something shows up after exit”. What the hell is that?