#include <stdio.h>

void ReverseString(char *s, int from, int to);

int main(int argc, const char * argv[]) {
    // insert code here...
    
    char s[] = "I am a student.";
    printf("%s\n", s);　　 // I am a student.
    
    int from = 0;
    int to = 0;
    
    for (int i = 0; i < sizeof(s); i ++) {
        if (s[i] == ‘ ‘ || s[i] == ‘\0‘) {
            to = i - 1;
            ReverseString(s, from, to);
            from = i + 1;
        }
    }
    printf("%s\n", s);　　// I ma a .tneduts
    
    ReverseString(s, 0, sizeof(s) - 2);
    printf("%s\n", s); 　　// student. a am I
    
    return 0;
}

void ReverseString(char *s, int from, int to) {
    while (from < to) {
        char t = s[from];
        s[from] = s[to];
        s[to] = t;
        from ++;
        to --;
    }
}