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Adding values to a C# array

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;



17 Answers
17

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).

new int

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);


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);



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

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;



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.

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.

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.

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.

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:t1",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

*/

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.

List<int>

Collection<int>

ToArray()

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();


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.

List<T>

var termsList = terms.ToList();

var terms = termsList.ToArray();

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(...);

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.

List<T>

List<T>

Times in ticks:

3 items

Array Resize Time: 6

List Add Time: 16

400 items

Array Resize Time: 305

List Add Time: 20

Just a different approach:

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

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

return scorecard.Split("!");


=

runs < 400

int terms = new int[400];

for(int runs = 0; runs < 400; runs++)

terms[runs] = value;



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.*/



/*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;



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