Question

I have this method that gives me IndexOutOfRangeException, can you guys help me to understand why?

public string FlipString(string inTxt)
    {
        StringBuilder outTxt = new StringBuilder();
        for (int i = inTxt.Length; i > 0; i--)
        {
            char ch = inTxt[i];
            outTxt.Append(ch);
        }
        Console.WriteLine(outTxt.ToString());
        return outTxt.ToString();
    }

The method has to be written like this (without the exception)

Answer 1

Arrays in C# are 0-based, not 1-based. You are iterating from n to 1, but you need to iterate from n-1 to 0:

for (int i = inTxt.Length - 1; i >= 0; i--)

On the other hand, if you just want to reverse the string, there’s a simpler solution using LINQ:

var reversed = new String(inTxt.Reverse().ToArray())