{"id":253,"date":"2022-01-01T16:01:59","date_gmt":"2022-01-01T09:01:59","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=253"},"modified":"2022-06-03T13:28:11","modified_gmt":"2022-06-03T06:28:11","slug":"csharp-foreach","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-foreach\/","title":{"rendered":"C# foreach"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the foreach statement to iterate over array elements.<\/p>\n\n\n\n

Using foreach with a single-dimensional array<\/h2>\n\n\n\n

To iterate over elements of a single-dimensional array<\/a>, you can use the for<\/a><\/code> statement. However, the foreach<\/code> statement provides a more simple and clean way to do so.<\/p>\n\n\n\n

The following uses the for<\/code> statement to iterate over elements of an array:<\/p>\n\n\n

int<\/span>[] scores = { 5<\/span>, 2<\/span>, 1<\/span>, 3<\/span>, 4<\/span> };\n\nfor<\/span> (int<\/span> i = 0<\/span>; i < scores.Length; i++)\n{\n    Console.Write($\"{scores[i]}<\/span> \"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
5<\/span> 2<\/span> 1<\/span> 3<\/span> 4<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we access the elements of the scores<\/code> array using an index specified by the variable i<\/code>. The variable i<\/code> starts at the index of the first element (0) and ends at the index of the last element (Length – 1). In each iteration, the variable i is increased by one. Therefore, the code iterates over all the array elements.<\/p>\n\n\n\n
The for statement works fine but it’s quite verbose and error-prone. <\/p>\n\n\n\n
For example, if you don’t control the variable i<\/code> properly, you’ll get an error of accessing an element at an invalid index.<\/p>\n\n\n\n
The following example uses the foreach<\/code> statement to iterate over the elements of the scores<\/code> array:<\/p>\n\n\n
int<\/span>[] scores = { 5<\/span>, 2<\/span>, 1<\/span>, 3<\/span>, 4<\/span> };\n\nforeach<\/span> (int<\/span> score in<\/span> scores)\n{\n    Console.Write($\"{score}<\/span> \"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
5 2 1 3 4<\/code><\/span><\/pre>\n\n\n
In this example, the foreach<\/code> statement processes the elements in the scores<\/code> array in increasing index order starting from the index 0<\/code> and ending with the index Lengh - 1<\/code>. In each iteration, the foreach<\/code> statement assigns the current element to the score<\/code> variable.<\/p>\n\n\n\n
Note that you can use the break<\/a><\/code> and continue<\/a><\/code> statements in the foreach<\/code> statement as the for<\/code> statement.<\/p>\n\n\n\n
The foreach<\/code> statement doesn’t allow you to change the array elements. For example, the following cause an error because it attempts to change the values of the array elements in a foreach<\/code> loop:<\/p>\n\n\n
int[] scores = { 5<\/span>, 2<\/span>, 1<\/span>, 3<\/span>, 4<\/span> };\n\nforeach<\/span> (int score in scores)\n{\n    score = score * 2<\/span>; \/\/ error<\/span>\n    Console.Write($\"{score} \"<\/span>);\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
To change the array element inside the loop, you need to use the for<\/code> statement. For example:<\/p>\n\n\n
int[] scores = { 5, 2, 1, 3, 4 };\n\nfor (int i = 0; i < scores.Length<\/span>; i<\/span>++)\n{\n    scores<\/span>[i<\/span>] *= 2;<\/span>\n    Console.Write<\/span>($\"{scores<\/span>[i<\/span>]} \");\n}<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
10 4 2 6 8<\/code><\/span><\/pre>\n\n\n
The following table summarizes the differences between foreach<\/code> and for<\/code> statements:<\/p>\n\n\n\n
foreach<\/th>for<\/th><\/tr><\/thead>
Clean and simple<\/td>Complex but flexible<\/td><\/tr>
Iterate all elements<\/td>Iterate all or a subset of elements<\/td><\/tr>
The elements are read-only<\/td>The elements are changeable<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Using the foreach statement with a multidimensional array <\/h2>\n\n\n\n
For a multidimensional array<\/a>, the foreach<\/code> statement increases the indices of the rightmost dimension first and then the next left dimension, and so on to the left. For example:<\/p>\n\n\n
int<\/span>[,] matrix =\n{\n    {1<\/span>,2<\/span>,3<\/span> },\n    {4<\/span>,5<\/span>,6<\/span> }\n};\n\nforeach<\/span>(var<\/span> e in<\/span> matrix)\n{\n    Console.Write($\"{e}<\/span> \"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
1<\/span> 2<\/span> 3<\/span> 4<\/span> 5<\/span> 6<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we have a two-dimensional array with two rows and three columns. The foreach<\/code> statement iterates elements from rows 0 to 1. For each row, it iterates the elements from columns 0 to 3.<\/p>\n\n\n\n
If you want to control the order in which to access the array elements, you can use a nested loop with the for<\/code> statement.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
  • Use the foreach<\/code> statement with one-dimensional arrays to iterate through the array elements.<\/li>
  • For a multidimensional array, use the for<\/code> statement to control the order in which you want to access the array elements.<\/li><\/ul>\n
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