Read no more than size of string with scanf()
Your array needs to be able to hold four chars, since it must also contain the 0-terminator. With that fixed, specifying a maximal length in the format,
scanf("%3s", string);ensures that scanf reads no more than 3 characters.
the safest way is to use
fgets(string, 4, stdin);here you can store maximum 3 characters including one space reserved for NULL ('\0') character.
You should use the width modifier of scanf() and set it to be one less than the size of your string, so that you ensure that space exists for the NULL terminator.
So, if you want to store "yes", you will firstly need a bigger array than the one you have; one with size 4, 3 characters plus 1 for the null terminator. Moreover, you should instruct scanf() to read no more than size - 1 characters, where size is the length of your array, thus 3 in this case, like this:
#include <stdio.h>int main(void){ char string[4]; scanf("%3s", string);}