#include <stdio.h>

void stringReverse(const char *s);

int main(void) {
    char string[] = "Hello world";

    printf("Original string: %s\n", string);
    printf("Reversed string: ");
    stringReverse(string);
    printf("\n");

    return 0;
}

void stringReverse(const char *s) {
    if (s[0] == '\0') {
        return;
    }
    
    stringReverse(&s[1]);
    putchar(s[0]);
}