What do these two pointers mean when reversing a sentence?

Question

I don't understand how words in the sentence is reversed, using the next code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
int main(void) {
    char *sent=(char*)calloc(120, sizeof(char*)); 
    puts("enter sentence:"); 
    gets(sent); 
    size_t n= strlen(sent); 
    char arr[n+1]; 
    char *p = arr; 
    char *q = sent + n; 
    while (q != sent){ 
       while (q != sent && isblank(*(q-1))) *p++ = *--q; 
        char *r = q; 
        while (r != sent && !isblank(*(r-1))) --r; 
        memcpy(p, r, q-r); 
        p+= q - r; 
        q = r; 
 }
 puts("original sentence:");
 puts(sent);
 puts("reversed sentence:");
 puts(arr);
 return 0;
  }

May somebody explain me what pointers *q and *r mean, please?

Answer 1

both, q and r, point to the end.

While q serves to process spaces (to point to the end of the word)
r is used to detect the beginning of a word.

Resp. memcpy(p, r, qr)
takes a word from r of length qr and places it in p