What does the keyword var do in C#?

The var keyword in C# enables implicit type declaration where the compiler automatically determines the variable's type based on the assigned value. This feature was introduced in C# 3.0 and provides cleaner code while maintaining type safety.

Syntax

Following is the syntax for using var keyword −

var variableName = initialValue;

The compiler infers the type from the initial value. Once declared, the variable behaves as if it were declared with its actual type.

How It Works

When you use var, the C# compiler performs type inference at compile time. The variable is strongly typed − it's not dynamic or loosely typed like in some scripting languages.

Using var with Basic Types

Example

using System;

class Program {
    static void Main(string[] args) {
        var myInt = 5;
        var myString = "Amit";
        var myDouble = 3.14;
        var myBool = true;
        
        Console.WriteLine("Integer: {0} (Type: {1})", myInt, myInt.GetType().Name);
        Console.WriteLine("String: {0} (Type: {1})", myString, myString.GetType().Name);
        Console.WriteLine("Double: {0} (Type: {1})", myDouble, myDouble.GetType().Name);
        Console.WriteLine("Boolean: {0} (Type: {1})", myBool, myBool.GetType().Name);
    }
}

The output of the above code is −

Integer: 5 (Type: Int32)
String: Amit (Type: String)
Double: 3.14 (Type: Double)
Boolean: True (Type: Boolean)

Using var with Arrays

Example

using System;

class Program {
    static void Main(string[] args) {
        var myIntArray = new int[] {65, 43, 88, 56};
        var myStringArray = new string[] {"Apple", "Banana", "Orange"};
        
        Console.WriteLine("Integer Array:");
        foreach(var val in myIntArray) {
            Console.WriteLine(val);
        }
        
        Console.WriteLine("\nString Array:");
        foreach(var item in myStringArray) {
            Console.WriteLine(item);
        }
    }
}

The output of the above code is −

Integer Array:
65
43
88
56

String Array:
Apple
Banana
Orange

Using var with Complex Types

Example

using System;
using System.Collections.Generic;

class Program {
    static void Main(string[] args) {
        var list = new List<string> {"C#", "Java", "Python"};
        var dictionary = new Dictionary<int, string> {{1, "First"}, {2, "Second"}};
        
        Console.WriteLine("List contents:");
        foreach(var item in list) {
            Console.WriteLine(item);
        }
        
        Console.WriteLine("\nDictionary contents:");
        foreach(var kvp in dictionary) {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }
    }
}

The output of the above code is −

List contents:
C#
Java
Python

Dictionary contents:
Key: 1, Value: First
Key: 2, Value: Second

Key Rules for var

Conclusion

The var keyword in C# provides implicit type declaration through compile-time type inference. It maintains type safety while reducing code verbosity, especially useful with complex generic types. Remember that var variables are still strongly typed − the compiler determines the exact type based on the initial assignment.