How to replace part of string by position?

Question

I have this string: ABCDEFGHIJ

I need to replace from position 4 to position 5 with the string ZX

It will look like this: ABC

Answer 1

It's better to use the String.substr().

Like this:

ReplString = GivenStr.substr(0, PostostarRelStr)
           + GivenStr(PostostarRelStr, ReplString.lenght());