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Using one array to populate a corresponding second array in C#

I am taking a class in c# programming and cannot figure out how to do the following. I have spent hours researching and nobody else seems to have the same issues.
The question is:
Write a function named, evenOrOdd, that will accept three parameters. The first parameter is the integer array used in the above function. The second parameter is the string array from step 2 and the third parameter is an integer indicating the size of the two arrays. This function will perform the following tasks:
This function will loop through the first array, checking each value to see if it is even or odd.
For each item in the integer array, the function will then place the appropriate value, “even” or “odd”, in the corresponding position of the string array.
Hint: Using the modulus operator, (also called the modulo), to divide the number by 2 will result in either a remainder of 0 or 1. A remainder of 0 indicates an even number and a remainder of 1 indicates an odd number. The modulus operator for all of the languages in this class is %.
After calling both functions, print the maximum number determined by findMax as well as the array index position of the largest number. Next, the program will loop through the two arrays and print the integer from integer array followed by the corresponding “even” or “odd” value from the string array
I do not understand how to populate the second string array with "even" or "odd".
The two arrays should be something like this:
array1 [1,2,3,4,5,6,7,8,9,10]
then run through a loop to determine if the values are even or odd and then assign the values to the second array so it is something like this:
array2 [odd,even,odd,even,odd,even,odd,even,odd,even]
I am confused how I "link" these two arrays together so that it know index of array 1=index of array 2.

You don't have to "link" the arrays together. You can use a variable which contains the current index and use it for both arrays. Like this:
for (int i = 0; i < array1.Length; i++){
//array1[i]...
//array2[i] = ...
}
This way, you can check if the number at index i in array 1 is even or odd and then modify the index i of array 2 accordingly.
Instead of array1.Length, you can also use the third argument of the method.

It looks like a code challenge. I highly recommend you find your own way to understand and solve this kind of problem and the fundamental concepts behind it as well.
One way to code the EvenOrOdd method:
public void EvenOrOdd(int[] numbers,
string[] natures, int size)
{
for(int i=0; i < size; i++)
if(numbers[i] % 2 == 0)
natures[i] = "even";
else
natures[i] = "odd";
}
One wat to code FindMax Function:
public static (int MaxValue, int MaxIndex) FindMax(int[] numbers)
{
int major = int.MinValue;
int majorIndex = -1;
for(int i=0; i < numbers.Length; i++)
if(numbers[i] > major)
{
major = numbers[i];
majorIndex = i;
}
return (major, majorIndex);
}
Check it in dotnetFiddle

How can I check for integers in list and print the index of them?

so my problem is that I don't know how to go forward in the list and print the next same integer if there is one.
Here is what I have at the moment:
while (list.Contains(input1))
{
Console.WriteLine(input1 + " is at index " + list.IndexOf(input1))
}
I am trying to list all of the integers that are in the list and print the index of them. But not remove after finding one of the integers (this was at least my first idea.).

IndexOf has an overload with two parameters, which allows you to start searching at a later position in the list.
Since this is obviously a learning exercise, I won't spoil it by providing the full code, but rather suggest that you try to implement the following algorithm:
Find the index of input starting at position 0.
If not found (i.e., IndexOf returns -1): we're done. Otherwise:
Print and remember that index.
Start again at step 1, but this time, don't start searching at 0 but at the index you remembered + 1.

You can do the following:
go through the list/array using for statement
for(int i=0; i < list.length; i++) // loop though list
then inside the loop check the value of the current item using if statement:
if(list[i] == input1)
//do smothing
The list[0] represent the first item in the array, which means the index is 0.
so in the example above the i will be the current index so long that you in the loop.
I didn't write the full code for learning purpose in reference to #Heinzi answer.
Hope that could be helpful!

This is an implementation possibility. It is longer than it has to be, but it makes it clearer for beginners how one could tackle this problem.
Since you wanted to only show numbers that come up more than once here is an implementation method. If you want to show numbers that come up only once too just erase everything about lastindex
List<int> yourlist = new List<int> { 1,1,1,1,1,11,2,3,3,4,4,5 };
int input = 0;
input = Convert.ToInt32(Console.ReadLine());
var index = yourlist.IndexOf(input);
//this checks if your input is in the list
var lastindex = yourlist.LastIndexOf(input);
//this does the same but it searches for the last implementation of your input
if (index != -1 && lastindex != index)
//this if checks if your number comes up more than once. IndexOf returns -1 if there is no occurence of your input
{
Console.Write($"the index of {input} is {index}");
for (int i = index+1; i <= yourlist.Count; i++)
//this loop takes the position of the first occurence of your number and then counts up from there
{
var tempindex = yourlist.IndexOf(input, i);
if (tempindex != -1)
//this if lets everything except -1 through
{
Console.Write($" and {tempindex}");
}
}
}
else
{
Console.WriteLine("your number cannot be found twice in the list");
}

Rearranging a string of numbers from highest to lowest C#

What I'm trying to do is to create a function that will rearrange a string of numbers like "1234" to "4321". I'm certain that there are many much more efficient ways to do this than my method but I just want to see what went wrong with what I did because I'm a beginner at programming and can use the knowledge to get better.
My thought process for the code was to:
find the largest number in the inputted string
add the largest number into a list
remove the largest number from the inputted string
find the largest number again from the (now shorter) string
So I made a function that found the largest number in a string and it worked fine:
static int LargestNumber(string num)
{
int largestnumber = 0;
char[] numbers = num.ToCharArray();
foreach (var number in numbers)
{
int prevNumber = (int) char.GetNumericValue(number);
if (prevNumber >= largestnumber)
{
largestnumber = prevNumber;
}
}
return largestnumber;
}
Now the rearranging function is what I am having problems with:
static List<int> Rearrange(string num)
{
List<int> rearranged = new List<int>(); // to store rearranged numbers
foreach (var number in num) //for every number in the number string
{
string prevnumber = number.ToString(); // the previous number in the loop
if (prevnumber == LargestNumber(num).ToString()) // if the previous number is the larges number in the inputted string (num)
{
rearranged.Add(Convert.ToInt32(prevnumber)); // put the previous number into the list
// removing the previous number (largest) from the inputted string and update the inputted string (which should be now smaller)
StringBuilder sb = new StringBuilder(num);
sb.Remove(num.IndexOf(number), 1);
num = sb.ToString();
}
}
return rearranged; // return the final rearranged list of numbers
}
When I run this code (fixed for concatenation):
var rearranged = Rearrange("3250");
string concat = String.Join(" ", rearranged.ToArray());
Console.WriteLine(concat);
All I get is:
5
I'm not sure what I'm missing or what I'm doing wrong - the code doesn't seem to be going back after removing '5' which i s the highest number then removing the next highest number/

Your issue is your if statement within your loop.
if (prevnumber == LargestNumber(num).ToString()
{
rearranged.Add(Convert.ToInt32(prevnumber));
//...
}
You only ever add to your List rearranged if the value of prevnumber is the largest value, which is false for every number but 5, so the only value that ever gets added to the list is 5.
That's the answer to why it's only returning 5, but I don't think that will make your method work properly necessarily. You're doing a very dangerous thing by changing the value of the collection you are iterating over (the characters in num) from within the loop itself. Other answers have been written for you containing a method that rearranges the numbers as you've described.

Your Rearrange method is returning List<int> when you try to write that to the console, the best it can do is write System.Collections.Generic.List1[System.Int32] (its type)
Instead of trying to write the list, convert it first into a data type that can be written (string for example)
eg:
var myList = Rearrange("3250");
string concat = String.Join(" ", myList.ToArray());
Console.WriteLine(concat);

Building on pats comment you could iterate through your list and write them to the console.
e.g.
foreach(var i in Rearrange(3250))
{
console.writeline(i.ToString());
}
or if you want to see the linq example.
using system.linq;
Rearrange(3250).foreach(i => console.writeline(i.ToString()));
--edit after seeing you're only getting '5' output
This is because your function only adds number to the list if they are the largest number in your list, which is why 5 is only being added and returned.

Your Rearrange method can be written easily using Array.Sort (or similar with (List<T>) :
int[] Rearrange(int num)
{
var arr = num.ToString ().ToCharArray ();
Array.Sort (arr, (d1, d2) => d2 - d1);
return Array.ConvertAll (arr, ch => ch - '0');
}

Just reading your first sentence
Does not test for integers
static int ReversedNumber(string num)
{
char[] numbers = num.ToCharArray();
Array.Sort(numbers);
Array.Reverse(numbers);
Debug.WriteLine(String.Concat(numbers));
return (int.Parse(String.Concat(numbers)));
}

Because your foreach loop within Rearrange method only loop through the original num. The algorithm doesn't continue to go through the new num string after you have removed the largest number.
You can find the problem by debugging, this foreach loop in Rearrange goes only 4 times if your input string is "3250".

whats wrong in this logic of finding longest common child of string

i came up with this logic to find longest common child of two strings of equal length but it runs successfuly only on simple outputs and fails others,pls guide me what i am doing wrong here.
String a, b;
int sum = 0;
int[] ar,br;
ar = new int[26];
br = new int[26];
a = Console.ReadLine();
b = Console.ReadLine();
for (int i = 0; i < a.Length; i++)
{
ar[(a[i] - 65)]++;
br[(b[i] - 65)]++;
}
for(int i =0;i<ar.Length;i++)
{
if (ar[i] <= br[i]) { sum += ar[i]; }
else sum += br[i];
}
Console.Write(sum);
Console.ReadLine();
output:
AA
BB
0 correct.
HARRRY
SALLY
2 correct
for both above input it runs but when i submit for evaluation it fails on their test cases.i cant access their testacase on which my logic fails.i wanna know where does my logic fails.

Your second loop is all wrong. It is simply finding the count of characters that occur in both the array and the count is only updated with the the no. of the common characters contained in the string containing the least no. of these common characters.
refer this link for the correct implementation.
http://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Longest_common_substring#Retrieve_the_Longest_Substring
Also convert your input to uppercase characters using String.ToUpper before you use the input string.

Get the sum of an array in C# but receiving int32 error

In general, I know that int32 errors mean that a string value is not getting converted for the console program. I have seen a lot of code trying to find the answer to this including the following stackoverflow questions (seen much more but these were most useful:
How to sum up an array of integers in C#
Error CS1501: I'm not overloading a Sum() method correctly
CS0019 Operator cannot be applied to operands of type 'bool' and 'int'
That being said, this is also a homework assignment, titled UsingSum.cs as seen in a couple of these links. The difference in mine and these is that I am trying to make it so that the user enters however many Integers they want, then they are added up. The entire assignment is written in link 2....
The problem: I keep getting either 0 or System.Int32[] instead of the sum, despite the changes I make.
I cannot use Linq.
Here is the code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace UsingSum
{
class Program
{
static void Main(string[] args)
{
int i;
int usrInput;
bool running = true;
//Enter Question Asking Loop w/ running=true
while (running)
{
Console.Write("Enter a number or enter 999 to exit: ");
int[] array1 = new int[0];
for (i = 0; i < array1.Length; i++)
{
usrInput = Convert.ToInt32(Console.ReadLine());
array1[i] = Convert.ToInt32(usrInput);
}
for (i = 0; i < array1.Length; i++)
{
Console.WriteLine(array1[i]);
}
/*If the user enters 999, calls Sum() and asks user to press any key to exit.
changes 'running' from true to false to exit the question loop*/
int exit = Convert.ToInt32 (Console.ReadLine());
if (exit == 999)
{
running = false;
Sum(array1);
}
}
//Loop complete
Console.WriteLine("Press any key to exit.");
Console.ReadLine();
}
public static void Sum(int[] numbers)
{
int [] sum1 = new int [0];
int sum2 = 0;
//Program accepts user responses with or w/o this loop...Int.32 error present both ways
//for (int a = 0; a < numbers.Length; ++a)
//sum1[a] = a;
//additional loop tried w/o the loop above/below;
//when used in the WriteLine w/ sum2 it displays 0, when used with sum1 or numbers Int.32 error
//Array.ForEach(sum1, delegate(int i) { sum2 += i; });
foreach (int i in numbers)
sum2 =+ i;
Console.WriteLine("The sum of the values in your array is: " + sum1);
/*tried changing 'numbers' to sum1, sum2, sum1.Convert.ToString(),sum2.Convert.ToString()
numbers.Convert.ToString(), also tried converting sum2 to a string.*/
}
}
}
Here is my final solution!
static void Main(string[] args)
{
AskUserForNumbers();
Console.WriteLine("Press any key to exit");
Console.ReadLine();
}
public static List<Int32> AskUserForNumbers()
{
bool running = true;
List<int> numbers = new List<int>();
while (running)
{
Console.Write("Enter a number or enter 999 to exit: ");
int inputValue;
var inputString = Console.ReadLine();
//Check for "999" which indicates we should display the numbers entered, the total and then exit our loop.
if (inputString == "999")
{
Console.WriteLine("The sum of the values in your array is: " + numbers.Sum());
running = false;
}
else if (Int32.TryParse(inputString, out inputValue) && inputValue > 0)
{
numbers.Add(inputValue);
}
else
{
Console.WriteLine("Please enter a whole number greater than 0");
}
}
return numbers;
}
}
}

A few problems:
First, you're always declaring your arrays as int[] array1 = new int[0];. This means that your code for actually getting the user input will never hit. Maybe you should try using a different collection type (List<int> maybe).
Second, you never perform any error checking when parsing the integer. That's bad practice. You should be using int.TryParse(string input, out result) to verify it was a valid number before adding it to the array.
Third, you are looping over the length of the array for inputs, meaning you will loop through however long the array is, and will continue doing so until the last input you have is the exit number (999).
Fourth, the input you get for the exit code is discarded (not added to the array to sum).
Just remember that programming is very procedural. There should be clear (logical) steps from point a to point b. In fact, imagine you are the program and you're asking a friend to give you numbers to sum up for him. Give him whatever information you think might be useful (such as the exit condition). Diagram the steps, and then try to translate that to code.
Edit: The main point is that an array (which has a fixed size) is NOT the tool for the job here. You're not actually filling the array with any data, so that's why the sum never happens. The culprit is here:
int[] array1 = new int[0]; // Instantiate a zero-length array? Can't hold any values
// Will never hit inside the loop here, because i < array1.Length (which is zero) will always be false.
for (i = 0; i < array1.Length; i++)
You need to either increase the size of the array to begin with (and either reuse the indexes or resize the array) or use an non-fixed collection (List, for example). Finally, when you pass array1 to the Sum method, array1 is empty because you declared it as a zero element array. That is why you always get a zero printing out. Like I said before, imagine you are the program, and actually run through all these steps, LINE BY LINE.
For example, you start in the loop. You prepare a miniature notebook to write down all the numbers your friend is telling you with no pages in it. For every page (and realize there are none) in the notebook, you ask your friend for a number. After you've gone through every page, you now go through every page again to read all the values he gave you (keep in mind he couldn't give you any numbers, since the notebook was empty). Then you ask him one more time for a number, and if it's 999 you tell him you're done and give him the sum of all the numbers you wrote down. If he didn't give you 999 as the number, you repeat the cycle.
Do you understand WHY it's not working now?

public static void Sum(int[] numbers)
{
int sum2 = 0;
foreach (int i in numbers)
sum2 =+ i;
Console.WriteLine("The sum of the values in your array is: " + sum2);
}

foreach (int i in numbers)
sum2 =+ i;
should become
foreach (int i in numbers)
sum2 += i;

Your problem is with your first for loop. You never will add items to your array because your
for (i = 0; i < array1.Length; i++)
Since you only add to your array1 array when you enter the loop, it won't ever increment. Since i = 0 and the array1.Length is 0 to start, i will never be less than the length.
Here is what I would suggest you do.
private static void Main(string[] args) {
var running = true;
var numbers = new List<int>();
//Enter Question Asking Loop w/ running=true
while (running) {
Console.Write("Enter a number or enter 999 to exit: ");
int inputValue;
var inputString = Console.ReadLine();
//Check for "999" which indicates we should display the numbers entered, the total and then exit our loop.
if (inputString == "999") {
//Display the numbers entered
foreach (var number in numbers) {
Console.WriteLine(number);
}
Console.WriteLine("The sum of the values in your array is: " + numbers.Sum());
running = false;
}
else if (Int32.TryParse(inputString, out inputValue) && inputValue > 0) {
//We have valid input, append it to our collection
numbers.Add(inputValue);
}
else {
//The user entered invalid data. Let them know.
Console.WriteLine("Please enter a whole number greater than 0");
}
}
//Loop complete
Console.WriteLine("Press any key to exit.");
Console.ReadLine();
}

You have several small mistakes here.
In your Sum method you are no longer using the array sum1, you're summing the values into sum2, but you're printing sum1. Your sum method should be (as described by Wiktor):
public static void Sum(int[] numbers)
{
int sum2 = 0;
foreach (int i in numbers)
sum2 += i;
Console.WriteLine("The sum of the values in your array is: " + sum2);
}
Also note that you used sum2 =+ i rather than sum2 =+ i. What that's saying is "set sum2 to be equal to the positive value of i" rather than, "add i to sum2.
Next, you have some issues in how you gather your input from the user. First off, arrays don't have a mutable size. The size that they have is fixed when they are created, and the array that you create to hold onto the values to sum up from the users is initialized to a size of 0. (int[] array1 = new int[0];) If you want to get a fixed number of values from the user you can put something other than 0 there for the array size, but based on the context it appears that you want the users to be able to add values until they enter 999 at which point you end. Since you don't know the size before hand you'll want to use a List<int> rather than an array, as you can just add items to it and it will magically grow to support the new items.
I would also suggest making a new method to get all of the values from the user, rather than embedding it in your Main method.
public static List<int> AskUserForNumbers()
{
List<int> numbers = new List<int>();
while(...)//todo determine end condition
{
string userInput = Console.ReadLine();
if(...)//todo determine if user is done
{
}
else
{
int nextNumber = ...;//todo parse user input
numbers.Add(nextNumber);
}
}
return numbers;
}
I'm not sure if it's a requirement for you to stop asking for numbers when the user enters 999 or if that's just what you did. if you have a choice, I would suggest using something different such as a blank line, 0, "quit", "exit", etc. 999 is a number that someone might want to sum.
As mentioned by SPFiredrake, it's best to use int.TryParse() to parse user input, that way if they enter a number that's not an int it won't crash, and you can tell the user that it was no good and they need to try again.