I know what the problem is.
We both made a silly mistake, that we use 20 to be the length of the string, just like ch[20], and also use STRCMP to compare to strings. As you know, the string should be ended with '\0', but as the length is 20, there will not be a char '\0' at the end of the string. So, when we use STRCMP, it gets the wrong value.
Maybe it can help you.

Yeah... I got wa6 just because I set a maxium number of people to 25... Thanks for your hint or sth. So everyone don't treasure the memory too much!