replacing string using extension method [closed]

Question

If I have string and I want to replace last character from that string with star for example.

I tried this

var myString = "ABCDEFGH";
myString.ReplaceCharacter(mystring.Length - 1, 1, "*"); 

public static string ReplaceCharacter(this string str, int start, int length, string replaceWith_expression)
{
    return str.Remove(start, length).Insert(start, replaceWith_expression);
}

I tried to use this extension method but this doesn't work. Why this doesn't work?

Answer 1

The method, as it is, replace the character, but you have to catch the result

myString = myString.ReplaceCharacter(myString.Length - 1, 1, "*");