UVa483 - Word Scramble

#include <stdio.h>#include <string.h>#define N 100void rev(char *str){    int i, len = strlen(str);    for (i = 0; i < len / 2; i++) {        str[i] = str[i] ^ str[len - 1 - i];        str[len - 1 - i] = str[len - 1 - i] ^ str[i];        str[i] = str[i] ^ str[len - 1 - i];    }}int main(){    int ch;    char buf[N];    int len = 0;    #ifndef ONLINE_JUDGE        freopen("d:\\UVa\\uva_in.txt", "r", stdin);    #endif    while ((ch = getchar()) != -1) {        if (' ' == ch || '\n' == ch) {            if (len) {                buf[len] = '\0';                rev(buf);                printf("%s", buf);            }            putchar(ch);            len = 0;        } else {            buf[len++] = ch;        }    }    return 0;}