>>927
#include <stdio.h>
#include <string.h>

int main()
{
char s[256];
int len;
int i;
char tmp;
printf(" input string: ");
scanf("%s",s);
len = strlen(s);
for (i = 0; i < len/2; ++i) {
tmp = s[i];
s[i] = s[len-1-i];
s[len-1-i] = tmp;
}
printf("output string: %s\n", s);
return 0;
}

別に奇偶判定の必要なかったが