{"id":470,"date":"2022-01-10T00:17:02","date_gmt":"2022-01-09T17:17:02","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=470"},"modified":"2022-06-03T13:15:47","modified_gmt":"2022-06-03T06:15:47","slug":"csharp-var","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-var\/","title":{"rendered":"C# var"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn to use the C# var<\/code> keyword to declare implicit-typed variables.<\/p>\n\n\n\n

Introduction to the C# var keyword<\/h2>\n\n\n\n

Starting from C# 3, you can use the var<\/code> keyword to declare implicit-typed variables. <\/p>\n\n\n\n

For example, the following declares a variable<\/a> and initializes its value as a literal string:<\/p>\n\n\n

string<\/span> message = \"Hi\"<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we use the string<\/code> type for the message<\/code> variable at the beginning of the declaration and a literal string as the initial value. The message<\/code> is an explicit-typed variable.<\/p>\n\n\n\n
However, from the value \"Hi\"<\/code>, the compiler can infer the variable as string<\/code>. Therefore, the explicit type at the beginning of the declaration is redundant. <\/p>\n\n\n\n
To avoid this redundancy, you can use the var<\/code> keyword in place of the explicit type at the beginning of the variable declaration like this:<\/p>\n\n\n
var<\/span> message = \"Hi\"<\/span>;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the message<\/code> is an implicit-typed variable. <\/p>\n\n\n\n
The var<\/code> keyword does not signal a special kind of variable. It’s syntactic shorthand for any type that the compiler can infer from the initialization of a variable declaration. <\/p>\n\n\n\n
Once the compiler can infer the variable type, it’s fixed and unchangeable. For example, you cannot assign an integer<\/a> to the message<\/code> variable like this:<\/p>\n\n\n
var<\/span> message = \"Hi\"<\/span>;\nmessage = 100<\/span>; \/\/ error<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
C# only allows you to use the var<\/code> keyword with a variable that includes an initialization. The following will result in an error:<\/p>\n\n\n
var<\/span> amount;<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Error:<\/p>\n\n\n
Implicitly typed variables must be initialized<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
  • Use the var<\/code> keyword for a variable with initialization from which the compiler can infer a type.<\/li>
  • Variables, which are declared with the var<\/code> keyword, are implicit-typed variables.<\/li><\/ul>\n
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In the above example, the var<\/code> is the shorthand for the string<\/a><\/code> type.  <\/p>\n\n\n\n