Write c function to reverse words in sentence (without using external arrays)

Here is a C function to reverse words in a sentence without using external arrays. This function uses two pointers to track the start and end of a word and then reverses the word in place.

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

void reverse(char* begin, char* end) {
    char temp;
    while (begin < end) {
        temp = *begin;
        *begin++ = *end;
        *end-- = temp;
    }
}

void reverseWords(char* s) {
    char* word_begin = s;
    char* temp = s;

    while (*temp) {
        temp++;
        if (*temp == '\0') {
            reverse(word_begin, temp - 1);
        } else if (*temp == ' ') {
            reverse(word_begin, temp - 1);
            word_begin = temp + 1;
        }
    }

    reverse(s, temp - 1);
}

int main() {
    char s[] = "Hello World";
    reverseWords(s);
    printf("%s", s);
    return 0;
}

This program works by first reversing each word in the sentence, and then reversing the entire sentence. This results in the words being in the original order, but the characters within each word are reversed.