字符串反转 单词保持有序

类似于异或运算

#include <stdio.h>

void swap_char(char *e1, char* e2) {
    char c;
    c = *e1, *e1 = *e2, *e2 = c;
}

char *reverse_str(char *s) {
    char *p = s;
    char *q = s;
    char *r = s;

    do {
        if (*p == ' ' || *p=='\0') {
            r = p;
            --p;
            while (q<p) {
                swap_char(q, p);
                ++q, --p;
            }

            q = r+1;
            p = r;
        }
        ++p;
    } while (*r != '\0'); 

    q = s;
    p = p-2;
    while (q<p) {
        swap_char(q, p);
        ++q, --p;
    }

    return s;
}

int main() {
    char s[] = "I am a student. ";

    puts(s);
    reverse_str(s);
    puts(s);

    return 0;
}