供参考
#include <stdio.h>
#include <string.h>
int main()
{
char in[512];
scanf("%s", in);
if(strcmp(in, "yes") == 0) printf("I know you said yes\n");
else if(strcmp(in, "no") == 0)printf("are you sure you want to say no?\n");
else printf("I dont know what are you speaking\n");
}