I mean even when I write one line of code in the function such as, return true or return false, without anything alse, it still returns number 1(in the case of true) or 0(in the case) not boolen value true or false. when I directly return true or false from code, the actual result is 1 or 0. I could solve this problem but becuase of this, I can not complete this kata.

It's a problem with your code, not a kata issue, if you return in both cases inside your loop, you're only testing the first char.