Please help me to check this code for string reverse in C

I'm writing this code to reverse the string, but somehow the last printf() seems can not print out the update string. I want to know why.

#include <stdio.h>

int main() {
    char x[] = "abcdefghijklmn";
    int j = sizeof(x);
    int i = 0;
    char t = 'a';
    printf("%s,%i\n", x, j / 2);

    for (; i < j / 2; i++) {
        t = x[i];
        x[i] = x[j - i - 1];
        x[j - i - 1] = t;
        printf("%c,%i,%i\n", x[i], i, j - i - 1);
    }

    printf("%s\n", x);

    return 0;
}