字符串翻转，单词内不翻转

字符串翻转，单词内不翻转。如I am from Chongqing->Chongqing from am I

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

void reverse(char *str, int beg, int end);
void reverseSentece(char *str);
int main()
{
    char str[128];
    gets_s(str,128);
    reverseSentece(str);
    puts(str);
    system("pause");
    return 0;
}

void reverse(char *str, int beg, int end)
{
    char temp;
    if(str == NULL)
        return;
    while(beg <= end)
    {
        temp = str[beg];
        str[beg] = str[end];
        str[end] = temp;
        beg++;
        end--;
    }
}

void reverseSentece(char *str)
{
    int beg = 0;
    int end = 0;
    if(str == NULL)
        return;
    //翻转整个句子
    reverse(str,0,strlen(str)-1);
    //局部翻转
    while(str[end] != '')
    {
        //找到单词的结束
        while(str[end] != '' && str[end] != ' ')
            ++end;
        //翻转一个单词
        reverse(str,beg,end-1);
        if(str[end] == '')
            break;
        ++end;
        beg = end;
    }
}