String reverse app not working- index outside the bounds of the array

Question

So, I've just started learning C#, and to be honest — I have no idea what I'm doing. I'm trying to make a string reverse app, and iv'e come up with this code:

string input = Console.ReadLine();
char[] wordArray = input.ToCharArray();
for(int i = input.Length; i >= 0; --i)
{
    Console.Write(wordArray[i]);
}

I've checked a bunch of different tutorials and documentations, and as far as I can tell from most of them, this should work, but it doesn't.

Whenever I run the app, I type in the word I want to reverse, and the app crashes. It shows an error that say "Index was outside the bounds of the array". I found better ways to reverse strings online using Array.Reverse(), but i would still like to understand why this error occurred. Like I said before, I'm not quite sure what I'm doing, and I'll be happy if anyone can explain this in layman's terms.

for(int i = input.Length-1; i >= 0; --i) arrays indexes starts in 0 and goes to lenght -1 — Pikoh
– Pikoh, Commented May 15, 2017 at 16:05

Samvel Petrosov · Accepted Answer · 2017-05-15 16:04:46Z

4

Your mistake is here int i = input.Length;. Your array is starting from 0 index and the last element is on index input.Length-1. So when you start from input.Lenght you are going out of bounds.

answered May 15, 2017 at 16:04

Samvel Petrosov

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Comments

Charles Mager · Accepted Answer · 2017-05-15 16:12:43Z

1

Your 'array' (a group of elements) contains each of the characters in your string.

Each of these elements can be accessed by its index, which starts at 0. So for the word word you would have:

0: 'w'
1: 'o'
2: 'r'
3: 'd'

The Length of this array is 4 - it has 4 elements - but you can see that the largest index isn't 4, it's 3.

Your loop counts from 4 down to 0 (as its Length is 4). When attempting to access the element with index 4, it throws the exception 'Index was outside the bounds of the array'.

The explanation as to how this works above should make this error message self-explanatory: 4 is outside the bounds of 0 to 3. You should start your loop from 3, which is input.Length - 1.

answered May 15, 2017 at 16:12

Charles Mager

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Comments

Stilet · Accepted Answer · 2017-05-15 16:06:28Z

-1

Maybe

string s = "123";
            string r = "";
            foreach (char c in s) r = c + r;
            Console.WriteLine(r);
            Console.ReadKey();

answered May 15, 2017 at 16:06

Stilet

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1 Comment

PaulF Over a year ago

OP says he knows better ways to reverse the string. What was asked was why the particular solution produced an error - this answer does not address the question.

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