倒序扣单词并不困难啊，维护两个 index ，一个头部一个尾部，寻找空格和非空格的边界就完了，哪用得着这么多 while

这么写结构清晰很多，并且含义还容易理解

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

void print_word(const char *str, size_t start, size_t stop) {
for (size_t i = start; i < stop; i++) {
// there is sth like %.*s but for simplicity ...
printf("%c", str[i]);
}
}

int main(int argc, char **argv) {
char test_str[] = " f test sentence here bla bla ";
size_t len = strlen(test_str) - 1;
size_t start = len;
size_t stop = len;
// flag just for proper trailing space ...
bool is_first_word = true;
for (size_t i = len; i > 0; i--) {
if (test_str[i] == ' ' && test_str[i - 1] != ' ') {
stop = i;
} else if (test_str[i] != ' ' && test_str[i - 1] == ' ') {
start = i;
if (is_first_word) {
is_first_word = false;
} else {
printf(" ");
}
print_word(test_str, start, stop);
}
}
return 0;
}