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;}