Adding values to a C# array

Question

Probably a really simple one this - I'm starting out with C# and need to add values to an array, for example:

int[] terms;

for(int runs = 0; runs < 400; runs++)
{
    terms[] = runs;
}

For those who have used PHP, here's what I'm trying to do in C#:

$arr = array();
for ($i = 0; $i < 10; $i++) {
    $arr[] = $i;
}

Answer 1

You can do this way -

int[] terms = new int[400];
for (int runs = 0; runs < 400; runs++)
{
    terms[runs] = value;
}

Alternatively, you can use Lists - the advantage with lists being, you don't need to know the array size when instantiating the list.

List<int> termsList = new List<int>();
for (int runs = 0; runs < 400; runs++)
{
    termsList.Add(value);
}

// You can convert it back to an array if you would like to
int[] terms = termsList.ToArray();

Edit: a) for loops on List<T> are a bit more than 2 times cheaper than foreach loops on List<T>, b) Looping on array is around 2 times cheaper than looping on List<T>, c) looping on array using for is 5 times cheaper than looping on List<T> using foreach (which most of us do).

Answer 2

Using Linq's method Concat makes this simple

int[] array = new int[] { 3, 4 };

array = array.Concat(new int[] { 2 }).ToArray();

result 3,4,2

Answer 3

If you're writing in C# 3, you can do it with a one-liner:

int[] terms = Enumerable.Range(0, 400).ToArray();

This code snippet assumes that you have a using directive for System.Linq at the top of your file.

On the other hand, if you're looking for something that can be dynamically resized, as it appears is the case for PHP (I've never actually learned it), then you may want to use a List instead of an int[]. Here's what that code would look like:

List<int> terms = Enumerable.Range(0, 400).ToList();

Note, however, that you cannot simply add a 401st element by setting terms[400] to a value. You'd instead need to call Add() like this:

terms.Add(1337);

Answer 4

By 2019 you can use Append, Prepend using LinQ in just one line

using System.Linq;

and then in NET 6 or NET 7 or NET 8 :

string[] fileLines = [];
terms = terms.Append(21);

or versions lower than NET 6.0

terms = terms.Append(21).ToArray();

Answer 5

Answers on how to do it using an array are provided here.

However, C# has a very handy thing called System.Collections

Collections are fancy alternatives to using an array, though many of them use an array internally.

For example, C# has a collection called List that functions very similar to the PHP array.

using System.Collections.Generic;

// Create a List, and it can only contain integers.
List<int> list = new List<int>();

for (int i = 0; i < 400; i++)
{
   list.Add(i);
}

Answer 6

Using a List as an intermediary is the easiest way, as others have described, but since your input is an array and you don't just want to keep the data in a List, I presume you might be concerned about performance.

The most efficient method is likely allocating a new array and then using Array.Copy or Array.CopyTo. This is not hard if you just want to add an item to the end of the list:

public static T[] Add<T>(this T[] target, T item)
{
    if (target == null)
    {
        //TODO: Return null or throw ArgumentNullException;
    }
    T[] result = new T[target.Length + 1];
    target.CopyTo(result, 0);
    result[target.Length] = item;
    return result;
}

I can also post code for an Insert extension method that takes a destination index as input, if desired. It's a little more complicated and uses the static method Array.Copy 1-2 times.

Answer 7

Based on the answer of Thracx (I don't have enough points to answer):

public static T[] Add<T>(this T[] target, params T[] items)
    {
        // Validate the parameters
        if (target == null) {
            target = new T[] { };
        }
        if (items== null) {
            items = new T[] { };
        }

        // Join the arrays
        T[] result = new T[target.Length + items.Length];
        target.CopyTo(result, 0);
        items.CopyTo(result, target.Length);
        return result;
    }

This allows to add more than just one item to the array, or just pass an array as a parameter to join two arrays.

Answer 8

You have to allocate the array first:

int [] terms = new int[400]; // allocate an array of 400 ints
for(int runs = 0; runs < terms.Length; runs++) // Use Length property rather than the 400 magic number again
{
    terms[runs] = value;
}

Answer 9

int ArraySize = 400;

int[] terms = new int[ArraySize];


for(int runs = 0; runs < ArraySize; runs++)
{

    terms[runs] = runs;

}

That would be how I'd code it.

Answer 10

15 years later... C# 12 brings us collection expressions, which is yet-another-way to add items to an array.

int[] x = [1, 2, 3]
x = [.. x, 4, 5, 6] // X is now 1,2,3,4,5,6

or for the original question, you can do something like this:

int[] terms = [];

for(int runs = 0; runs < 400; runs++)
{
    terms = [.. terms, runs];
}

Answer 11

You can't just add an element to an array easily. You can set the element at a given position as fallen888 outlined, but I recommend to use a List<int> or a Collection<int> instead, and use ToArray() if you need it converted into an array.

Answer 12

If you really need an array the following is probly the simplest:

using System.Collections.Generic;

// Create a List, and it can only contain integers.
List<int> list = new List<int>();

for (int i = 0; i < 400; i++)
{
   list.Add(i);
}

int [] terms = list.ToArray();

Answer 13

C# arrays are fixed length and always indexed. Go with Motti's solution:

int [] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
    terms[runs] = value;
}

Note that this array is a dense array, a contiguous block of 400 bytes where you can drop things. If you want a dynamically sized array, use a List<int>.

List<int> terms = new List<int>();
for(int runs = 0; runs < 400; runs ++)
{
    terms.Add(runs);
}

Neither int[] nor List<int> is an associative array -- that would be a Dictionary<> in C#. Both arrays and lists are dense.

Answer 14

one approach is to fill an array via LINQ

if you want to fill an array with one element you can simply write

string[] arrayToBeFilled;
arrayToBeFilled= arrayToBeFilled.Append("str").ToArray();

furthermore, If you want to fill an array with multiple elements you can use the previous code in a loop

//the array you want to fill values in
string[] arrayToBeFilled;
//list of values that you want to fill inside an array
List<string> listToFill = new List<string> { "a1", "a2", "a3" };
//looping through list to start filling the array

foreach (string str in listToFill){
// here are the LINQ extensions
arrayToBeFilled= arrayToBeFilled.Append(str).ToArray();
}

Answer 15

Array Push Example

public void ArrayPush<T>(ref T[] table, object value)
{
    Array.Resize(ref table, table.Length + 1); // Resizing the array for the cloned length (+-) (+1)
    table.SetValue(value, table.Length - 1); // Setting the value for the new element
}

Answer 16

int[] terms = new int[10]; //create 10 empty index in array terms

//fill value = 400 for every index (run) in the array
//terms.Length is the total length of the array, it is equal to 10 in this case 
for (int run = 0; run < terms.Length; run++) 
{
    terms[run] = 400;
}

//print value from each of the index
for (int run = 0; run < terms.Length; run++)
{
    Console.WriteLine("Value in index {0}:\t{1}",run, terms[run]);
}

Console.ReadLine();

/*Output：

Value in index 0: 400
Value in index 1: 400
Value in index 2: 400
Value in index 3: 400
Value in index 4: 400
Value in index 5: 400
Value in index 6: 400
Value in index 7: 400
Value in index 8: 400
Value in index 9: 400
*/

Answer 17

If you don't know the size of the Array or already have an existing array that you are adding to. You can go about this in two ways. The first is using a generic List<T>: To do this you will want convert the array to a var termsList = terms.ToList(); and use the Add method. Then when done use the var terms = termsList.ToArray(); method to convert back to an array.

var terms = default(int[]);
var termsList = terms == null ? new List<int>() : terms.ToList();

for(var i = 0; i < 400; i++)
    termsList.Add(i);

terms = termsList.ToArray();

The second way is resizing the current array:

var terms = default(int[]);

for(var i = 0; i < 400; i++)
{
    if(terms == null)
        terms = new int[1];
    else    
        Array.Resize<int>(ref terms, terms.Length + 1);
    
    terms[terms.Length - 1] = i;
}

If you are using .NET 3.5 Array.Add(...);

Both of these will allow you to do it dynamically. If you will be adding lots of items then just use a List<T>. If it's just a couple of items then it will have better performance resizing the array. This is because you take more of a hit for creating the List<T> object.

Times in ticks:

3 items

Array Resize Time: 6

List Add Time: 16

400 items

Array Resize Time: 305

List Add Time: 20

Answer 18

I will add this for a another variant. I prefer this type of functional coding lines more.

Enumerable.Range(0, 400).Select(x => x).ToArray();

Answer 19

This seems like a lot less trouble to me:

var usageList = usageArray.ToList();
usageList.Add("newstuff");
usageArray = usageList.ToArray();

Answer 20

Just a different approach:

int runs = 0; 
bool batting = true; 
string scorecard;

while (batting = runs < 400)
    scorecard += "!" + runs++;

return scorecard.Split("!");

Answer 21

You can't do this directly. However, you can use Linq to do this:

List<int> termsLst=new List<int>();
for (int runs = 0; runs < 400; runs++)
{
    termsLst.Add(runs);
}
int[] terms = termsLst.ToArray();

If the array terms wasn't empty in the beginning, you can convert it to List first then do your stuf. Like:

    List<int> termsLst = terms.ToList();
    for (int runs = 0; runs < 400; runs++)
    {
        termsLst.Add(runs);
    }
    terms = termsLst.ToArray();

Note: don't miss adding 'using System.Linq;' at the begaining of the file.

Answer 22

int[] terms = new int[400];

for(int runs = 0; runs < 400; runs++)
{
    terms[runs] = value;
}

Answer 23

         static void Main(string[] args)
        {
            int[] arrayname = new int[5];/*arrayname is an array of 5 integer [5] mean in array [0],[1],[2],[3],[4],[5] because array starts with zero*/
            int i, j;


          /*initialize elements of array arrayname*/
            for (i = 0; i < 5; i++)
            {
                arrayname[i] = i + 100;
            }

             /*output each array element value*/
            for (j = 0; j < 5; j++)
            {
                Console.WriteLine("Element and output value [{0}]={1}",j,arrayname[j]);
            }
            Console.ReadKey();/*Obtains the next character or function key pressed by the user.
                                The pressed key is displayed in the console window.*/
        }

Answer 24

            /*arrayname is an array of 5 integer*/
            int[] arrayname = new int[5];
            int i, j;
            /*initialize elements of array arrayname*/
            for (i = 0; i < 5; i++)
            {
                arrayname[i] = i + 100;
            }

Answer 25

To add the list values to string array using C# without using ToArray() method

        List<string> list = new List<string>();
        list.Add("one");
        list.Add("two");
        list.Add("three");
        list.Add("four");
        list.Add("five");
        string[] values = new string[list.Count];//assigning the count for array
        for(int i=0;i<list.Count;i++)
        {
            values[i] = list[i].ToString();
        }

Output of the value array contains:

one

two

three

four

five

Answer 26

You can do this is with a list. here is how

List<string> info = new List<string>();
info.Add("finally worked");

and if you need to return this array do

return info.ToArray();

Answer 27

Here is one way how to deal with adding new numbers and strings to Array:

int[] ids = new int[10];
ids[0] = 1;
string[] names = new string[10];

do
{
    for (int i = 0; i < names.Length; i++)
    {
        Console.WriteLine("Enter Name");
        names[i] = Convert.ToString(Console.ReadLine());
        Console.WriteLine($"The Name is: {names[i]}");
        Console.WriteLine($"the index of name is: {i}");
        Console.WriteLine("Enter ID");
        ids[i] = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine($"The number is: {ids[i]}");
        Console.WriteLine($"the index is: {i}");
    }


} while (names.Length <= 10);