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Index was outside the bounds of the array. and even my teacher doesn't know the solution

I'm trying to make a scan of an array where it follows the index with the numbers inside and I don't understand why it gives me this exception. I cant add any more details its a pretty straight forward question.
using System;
public class Program
{
public static bool IsPerfect(int[] arr)
{
int next=0, done=0,i;
while (done == 0)
{
i = arr[next];
arr[next] = 10;
next = arr[i];
if (i == 0)
done = 1;
}
for(int j = 0; j < arr.Length; j++)
if (arr[j] != 10)
return false;
return true;
}
public static void Main()
{
int[] arr = { 3, 0, 1, 4, 2 };
if (IsPerfect(arr) == true)
Console.WriteLine("is perfect");
if (IsPerfect(arr) == false)
Console.WriteLine("boooo");
}
}

You are not specifying the functioning for duplicates... Use a method to check for duplicates and as soon as you encounter a duplicate element exit the loop... It will work fine! 👍

ok for anyone intrested the problem was lying in the second if, and the "next = arr[i];" the first i changed because it made more sense and the second and main problem was the other if. because i had the second condition it ran the method twice and with the changed values it returned an error.
the solution was to put else instead.

Reverse engineering: we mark visited items and if all items are visted, then we have a "Perfect" array.
Problem: we mark item with 10 which can be an index (what if array has, say, 15 items)?
Solution: let's mark by -1 (definitely not an index - an array can have negative number of items) and check if item has been marked:
Tricky moment: we should assign -1 to the current arr[i] item but use its initial value to be assigned to i. Sure, we can save i and put it as
for (int i = 0; i >= 0 && i < arr.Length; ) {
int nextI = arr[i];
arr[i] = i;
i = nextI;
}
but let's put in a short modern way: (i, arr[i]) = (arr[i], -1);
Code:
public static bool IsPerfect(int[] arr) {
// In public method we must be ready for any input; null included
if (arr == null)
return false; // or throw new ArgumentNullException(nameof(arr));
// Do we have a valid array?
for (int i = 0; i < arr.Length; ++i)
if (arr[i] < 0 || arr[i] >= arr.Length)
return false;
// Note the condition: we read the next item - arr[i] -
// if and only if i is within range
// Note, that we have nothing to increment / decrement
for (int i = 0; i >= 0 && i < arr.Length; )
(i, arr[i]) = (arr[i], -1); // note the assignment: both i and arr[i] in one go
// We have marked all that we could.
// Do we have unmarked items?
for (int i = 0; i < arr.Length; ++i)
if (arr[i] != -1) // ... yes, we have and thus
return false; // arr is not perfect
return true;
}
Please, fiddle

Bring multiple 2d arrays [][] on same length

i have a huge Problem when dealing with jagged arrays [][].
I wrote a program that interacts with lots of CSV-files. It will read them and then compare them. Now i have a problem if Array A has the dimension of 10 Rows and 10 Columns but Array B only has the dimension of 5 Rows and 5 Columns. I get the "out of range" on array B. This is only an example it gets even worse if i have a array which has different amount of Rows in each Column...
I tried checking for "null" but this doesnt work since i get the "out of range" once it tries to acess the field...
Now i have 2 theories to solve the problem:
A.)Check for "out of range" in Array B and if so fill Array A at the same field with a "0"
B.) Check if Array A and Array B has same dimension and if not fill the array with lesser amount with "0" so that it has the same amount
On both solutions i have absolutely no clue how to do this in C#... I am always getting the out of range...
What i currently do for 1 array is:
for (int b = CSV_Statistiken.Length - 1; b >= 0; b--)
{
for (int a = 0; a < CSV_Statistiken[b].Length; a++)
{
CSV_Statistiken[b][a] = 1;
}
}
so i get the dimension of the array and iterate through it, setting every value to 1. But how do i deal with my problem with 2 arrays?
I researched a bit but couldnt find any solution to this =/
Thanks in advance
Edit: What i am trying to do for examlple:
for (int i = 0; i < number; i++) //runs through every File existing
{
NextFile = fold.Filepath + "\\" + files[i].ToString();
file = new FileInfo(#NextFile);
max_Rows = 0;
max_Col = 0;
CSV_temp = ReadCSV(file, ref max_Rows, ref max_Col); // reads the next file to an arraay [][] and saves the size of this array in max_col/ max_rows
MAX_Col_Total = GetHighestValues(ref MAX_Col_Total, max_Col);
MAX_Rows_Total = GetHighestValues(ref MAX_Rows_Total, max_Rows);
for (int j = 0; j < MAX_Col_Total; j++) //runs thrugh the max amount of cols found
{
for (int k = MAX_Rows_Total - 1; k >= 0; k--) //runs through the max mount of rows found
{
if (CSV_temp.GetLength(0) >= j && CSV_temp.GetLength(1) >= k)//Checks if Field exists -> does NOT work!
{
if (CSV_temp[k][j] > (Threshhold))) //
{
do something
}
}
else
{
// Field doesnt exists -> do something else
}
}
}
}

You can check Lengths of two arrays in for loops:
for (int a = 0; a < array1.Length && a < array2.Length; a++)
{
for (int b = 0; b < array1[a].Length && b < array2[a].Length; b++)
{
//compare
}
}
Now your loops never go outside of any array index and you won't get IndexOutOfRangeException.
EDIT:
var biggestLength1 = Math.Max(array1.Length, array2.Length);
for (int a = 0; a < biggestLength1; a++)
{
var biggestLength2 = 0;
if (array1.Length > a && array2.Length > a)
{
biggestLength2 = Math.Max(array1[a].Length, array2[a].Length);
}
else
{
biggestLength2 = array1.Length > a ? array1.Length : array2.Length;
}
for (int b = 0; b < biggestLength2; b++)
{
if (a < array1.Length &&
a < array2.Length &&
b < array1[a].Length &&
b < array2[a].Length)
{
// every array has enough elements count
// you can do operations with both arrays
}
else
{
// some array is bigger
}
}
}

Adding array to a list how to stop it being the last iteration data? [duplicate]

This question already has answers here:
C# dictionary value clearing out when I clear list previously assigned to it....why?
(6 answers)
Closed 6 years ago.
I am trying to create a list of an array of 2 items. The problem I have is the final iteration in my loop sets all the list's arrays to the same (my guess is due to a reference?). I was wondering how I can prevent this from happening.
This is what I am trying to do:
PathTiles[] links = new PathTiles[2];
int j;
for(int i = 0; i < path.Count; i++)
{
if(i+1 < path.Count)
{
links[0] = path[i];
links[1] = path[i];
for(j = i+1; j < path.Count; j++)
{
if(path[j].x == links[1].x && Mathf.Abs(path[j].y-links[1].y) == 1)
{
links[1] = path[j];
i = j;
}
else
{
break;
}
}
validPath.Add(links);
for(int k = 0; k < validPath.Count;k++)
{
Debug.Log(validPath[k].x+", "+validPath[k].y);
}
Debug.Log("=====");
}
}
So the console shows this:
0, 0
=====
1, 1 <-- why did this become 1, 1 and not stay as 0, 0
1, 1
=====
Does any one know how I can retain the first data value and not have it overwritten? I am currently under the impression it is because it stores a reference and so I changed the values, but I don't know how to stop it doing that.

Try adding the PathTiles[] links = new PathTiles[2]; within the 1st for loop statement. As you said this is a problem of references. As you were addiing the same modified links to the list. the 1st data value is overwritten.
int j;
for (int i = 0; i < path.Count; i++)
{
PathTiles[] links = new PathTiles[2]; //<-- here
if (i + 1 < path.Count)
{
links[0] = path[i];
links[1] = path[i];
...

Cannot find duplicates in array [duplicate]

This question already has answers here:
How do I check if my array has repeated values inside it?
(8 answers)
Find duplicates between arrays
(16 answers)
Closed 8 years ago.
I need to find duplicate numbers in this method. Ive tried this, but i think im missing something. anyone can see what I'm doing wrong.
public bool FindDublicate(int[] a)
{
bool svar = true;
for (int i = 0; i < a.Length; i++)
{
for (int j = i; j < a.Length - 1; j++)
{
if (a[j] == a[j + 1])
{
svar = true;
}
else return false;
}
}
return svar;
}

If you are only interested in knowing whether your array contains duplicate or not you can do:
return a.Distinct().Count() != a.Length;

check if array is chronological

I have a list of integer arrays, and i want to check for each array if the array if chronological, if it is not I want it to be removed from the list.
At the moment I do it like this:
for (int i = 0; i < allXcombis.Count(); i++)
{
bool remove = false;
for (int j = 0; j < allXcombis[i].Length; j++)
{
if (allXcombis[i].Count() - 1 > j)
if (allXcombis[i][j] != allXcombis[i][j + 1] - 1)
remove = true;
}
if (remove)
allXcombis.Remove(allXcombis[i]);
}
but I am not really happy with this code, I think it can be done easier.

First, I would probably extract the checking that the array is “chronological” into its own method and made it more efficient, by returning from the loop early:
bool IsChronological(int[] array)
{
for (int i = 0; i < array.Length - 1; i++)
{
if (array[i] != array[i + 1] - 1)
return false;
}
return true;
}
And then I would simply use RemoveAll():
allXcombis.RemoveAll(a => !IsChronological(a));
This way, you get concise, readable code and you don't have to worry about indexes in the list (as others mentioned, you have a bug in your code, because you're not careful about the indexes).

When you are removing from list inside loop, you need either to fix loop variable or to loop backwards. Then, you don't need () after Count. And you can break from loop after assigning remove = true, this will improve performance.
for (int i = allXcombis.Count - 1; i >= 0; i--)
{
bool remove = false;
for (int j = 0; j < allXcombis[i].Length; j++)
{
if (allXcombis[i].Length - 1 > j)
{
if (allXcombis[i][j] != allXcombis[i][j + 1] - 1)
{
remove = true;
break;
}
}
}
if (remove)
allXcombis.Remove(allXcombis[i]);
}

If by chronological you mean sorted, then you need to check < not !=.
Also you can simplify some things. The most important is when you find that it's not sorted to break out of the inner loop, so that you don't keep iterating.
Also you need to decrease i when you remove, because you'll skip some arrays otherwise (say if i = 2 and you remove the second array, then the third array becomes second, but i will be 3 on the next iteration, so you'll skip it)
for (int i = 0; i < allXcombis.Count; i++)
{
for (int j = 0; j < allXcombis[i].Length-1; j++)
{
if (allXcombis[i][j] > allXcombis[i][j + 1] - 1)
{
allXcombis.Remove(allXcombis[i]);
i--;
break;
}
}
}

I agree with svick in the use of a dedicated method like he proposed "IsChronological" but I would like to add a little bit of security and performance to this method:
bool IsChronological(int[] array)
{
bool result = ((array == null) || (array.Length == 0)) ? false : true; //Null or empty arrays are not chronological by definition (also avoid exceptions)
if (result)
{
result = (array.Length == 1) ? true : false; //Arrays with only one element are chronological by definition
if (!result)
{
int length = array.Length - 1;
int index = 0;
while ((index < length) && (array[index] == array[index] + 1))
index++;
result = (index == array.length);
}
}
return result;
}