C# Language Tutorial => var

Example

An implicitly-typed local variable that is strongly typed just as if the user had declared the type. Unlike other variable declarations, the compiler determines the type of variable that this represents based on the value that is assigned to it.

var i = 10; // implicitly typed, the compiler must determine what type of variable this is
int i = 10; // explicitly typed, the type of variable is explicitly stated to the compiler

// Note that these both represent the same type of variable (int) with the same value (10).

Unlike other types of variables, variable definitions with this keyword need to be initialized when declared. This is due to the var keyword representing an implicitly-typed variable.

var i;
i = 10;

// This code will not run as it is not initialized upon declaration.

The var keyword can also be used to create new datatypes on the fly. These new datatypes are known as anonymous types. They are quite useful, as they allow a user to define a set of properties without having to explicitly declare any kind of object type first.

Plain anonymous type

var a = new { number = 1, text = "hi" };

LINQ query that returns an anonymous type

public class Dog
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public class DogWithBreed
{
    public Dog Dog { get; set; }
    public string BreedName  { get; set; }
}

public void GetDogsWithBreedNames()
{
    var db = new DogDataContext(ConnectString);
    var result = from d in db.Dogs
             join b in db.Breeds on d.BreedId equals b.BreedId
             select new 
                    {
                        DogName = d.Name,
                        BreedName = b.BreedName
                    };

    DoStuff(result);
}

You can use var keyword in foreach statement

public bool hasItemInList(List<String> list, string stringToSearch)
{
    foreach(var item in list)
    {
        if( ( (string)item ).equals(stringToSearch) )
            return true;
    }

    return false;
}

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C# Language Keywords var

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