Reverse the words of a sentence in place in C Solution, output & explanation

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

static void rev(char *l, char *r) {
    while (l < r) {
        char t = *l;
        *l++ = *r;
        *r-- = t;
    }
}

void reverse_words(char *s) {
    size_t n = strlen(s);
    if (n == 0)
        return;
    rev(s, s + n - 1);                  /* 1. reverse the whole sentence */
    for (char *w = s; *w; ) {           /* 2. reverse each word back */
        while (*w == ' ')
            w++;
        char *e = w;
        while (*e && *e != ' ')
            e++;
        if (e > w)
            rev(w, e - 1);
        w = e;
    }
}

int main(void) {
    char s[] = "pointers are fun";
    reverse_words(s);
    printf("%s\n", s);
    return 0;
}

fun are pointers