C# System.IndexOutOfRangeException or cant convert to Long

Question

I'm kinda of having this error:

"System.IndexOutOfRangeException: Index was out of the Array"

When I change int=1 to long=1 it says it can't convert long to int.

I'm trying to save all output of N into the Array and show at the end what is saved into arrays.

static void Main(string[] args)
{
    int a = 0;
    a = Convert.ToInt64(Console.ReadLine());

    int[] array = new int[a];

    if (a == 0)
    {
        Console.WriteLine("Falsche eingabe.");
    }
    else
    {
        long n = 1;
        for (int i = 1; i <= array.Length; i++)
        {
            n *= i;
            array[i] = n;

            Console.WriteLine("N: " + i + " Fakultät von N: " + array[i]);
        }
    }
    Console.ReadKey();
}

longs are bigger than ints, if you had a long that was bigger than int and you tried to convert it to an int, what would you expect to happen? — Stuart, Aug 15 '17 at 16:27
`i <= array.Length` is wrong - if `i` is `array.Length` it means it's out of range as arrays are 0 based — Jakub Dąbek, Aug 15 '17 at 16:28
I think knowing if the language you are coding in is zero-indexed or one-indexed is pretty primitive - if you already know that then please learn to debug your problems more carefully. — crazyGamer, Aug 15 '17 at 16:30
@JakubDąbek it makes sense, I change array.Length to just "a". It underlimes the "array[i] = n;" and says the same problem asit was before. — , Aug 15 '17 at 17:51

score 1 · Accepted Answer · answered Aug 15 '17 at 16:29

1

Indexes of arrays begin from 0 not from one. Therefore in your for loop, i <= array.Length, when i is equal to the length you enter and try array[array.Length] which throws the exception. Change to:
```
for (int i = 0; i < array.Length; i++)
```
Reason indexes are zero based is that the language is based on C where an array is a pointer to the location that was allocated for the array:
```
int *arrayPointer;
```
And then to go through the array one needs to go to arrayPointer + sizeof(int)*i. So for the first position of the array i should start from zero
In addition this line doesn't compile:
```
a = Convert.ToInt64(Console.ReadLine());
```
a is of type int while you are converting to long. Use ToInt32

answered Aug 15 '17 at 16:29

Gilad Green

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without array[i] = n; line everything works fine without any problem. It works also when i define a as a long and int64 sane as int62 why? – Aug 15 '17 at 17:53
as long I write array [i] in console.writeline for example Console.WriteLine("N: " + array[i] + " Fakultät von N: " + n); I get that error.. – Aug 15 '17 at 17:55
For the reason I explain - debug and see. At the last iteration of the loop, when `i` equals `array.Length` you get the exception. Because of out of bounds. – Gilad Green Aug 15 '17 at 17:56
@eXme - Did you manage to solve it? – Gilad Green Aug 16 '17 at 08:17
no I did not solved the problem. I also tryed same thing with list and having almost same problem System.ArgumentOutOfRangeException dont understand yet, how to solve the problem. – Aug 16 '17 at 11:44
@eXme - Did you change the loop condition as I suggested? – Gilad Green Aug 16 '17 at 11:44
no but i found the problem it was in for (int i = 1; i <= array.Length; i++) and in Console.WriteLine("N: " + i + " Fakultät von N: " + `array[i]`); my i start from 1 and it should start from 0 in array because there is no array[1] in the first loop and only 0 :D so if i declate variable j = 0; and then add array[j++] it works of course as it should be, the fak... part took me whole day lol :D – Aug 16 '17 at 14:22
@eXme - Yes - because of what I said before. when you access list[i] in a place that is not in the array. – Gilad Green Aug 16 '17 at 14:23
I didnt get it, im not that advanced in yet doing it for some days only :) but thanks tho if you tho it was like that. – Aug 16 '17 at 14:25

C# System.IndexOutOfRangeException or cant convert to Long

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