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C# Arrays


Create an Array

Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.

To declare an array, define the variable type with square brackets:

string[] cars;

We have now declared a variable that holds an array of strings.

To insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces:

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

To create an array of integers, you could write:

int[] myNum = {10, 20, 30, 40};

Access the Elements of an Array

You access an array element by referring to the index number.

This statement accesses the value of the first element in cars:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars[0]);
// Outputs Volvo

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Note: Array indexes start with 0: [0] is the first element. [1] is the second element, etc.


Change an Array Element

To change the value of a specific element, refer to the index number:

Example

cars[0] = "Opel";

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
Console.WriteLine(cars[0]);
// Now outputs Opel instead of Volvo

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Array Length

To find out how many elements an array has, use the Length property:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Console.WriteLine(cars.Length);
// Outputs 4

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Loop Through an Array

You can loop through the array elements with the for loop, and use the Length property to specify how many times the loop should run.

The following example outputs all elements in the cars array:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (int i = 0; i < cars.Length; i++) 
{
  Console.WriteLine(cars[i]);
}

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The foreach Loop

There is also a foreach loop, which is used exclusively to loop through elements in an array:

Syntax

foreach (type variableName in arrayName) 
{
  // code block to be executed
}

The following example outputs all elements in the cars array, using a foreach loop:

Example

string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
foreach (string i in cars) 
{
  Console.WriteLine(i);
}

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The example above can be read like this: for each string element (called i - as in index) in cars, print out the value of i.

If you compare the for loop and foreach loop, you will see that the foreach method is easier to write, it does not require a counter (using the Length property), and it is more readable.


Sort Arrays

There are many array methods available, for example Sort(), which sorts an array alphabetically or in an ascending order:

Example

// Sort a string
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Array.Sort(cars);
foreach (string i in cars)
{
  Console.WriteLine(i);
}
// Sort an int
int[] myNumbers = {5, 1, 8, 9};
Array.Sort(myNumbers);
foreach (int i in myNumbers)
{
  Console.WriteLine(i);
}

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System.Linq Namespace

Other useful array methods, such as Min, Max, and Sum, can be found in the System.Linq namespace:

Example

using System;
using System.Linq;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int[] myNumbers = {5, 1, 8, 9};
      Console.WriteLine(myNumbers.Max());  // returns the largest value
      Console.WriteLine(myNumbers.Min());  // returns the smallest value
      Console.WriteLine(myNumbers.Sum());  // returns the sum of elements
    }
  }
}

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You will learn more about other namespaces in a later chapter.


Other Ways to Create an Array

If you are familiar with C#, you might have seen arrays created with the new keyword, and perhaps you have seen arrays with a specified size as well. In C#, there are different ways to create an array:

// Create an array of four elements, and add values later
string[] cars = new string[4];

// Create an array of four elements and add values right away 
string[] cars = new string[4] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements without specifying the size 
string[] cars = new string[] {"Volvo", "BMW", "Ford", "Mazda"};

// Create an array of four elements, omitting the new keyword, and without specifying the size
string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};

It is up to you which option you choose. In our tutorial, we will often use the last option, as it is faster and easier to read.

However, you should note that if you declare an array and initialize it later, you have to use the new keyword:

// Declare an array
string[] cars;

// Add values, using new
cars = new string[] {"Volvo", "BMW", "Ford"};

// Add values without using new (this will cause an error) cars = {"Volvo", "BMW", "Ford"};

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C# 练习

Test Yourself With 练习

Exercise:

Create an array of type string called cars.

  = {"Volvo", "BMW", "Ford", "Mazda"};

Start the Exercise





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