Default parameters

Learn to define parameters with default values.

Default parameters

A parameter can be given a default value; this is called a default parameter. The declaration adds = value to the parameter: static void Greet(string name = "Friend"). If no argument is given at the call, this value is used.

For example, Greet() uses "Friend" for name; Greet("Ayşe") uses the given argument. Default parameters add flexibility at the call site.

Default and ordering

Default parameters must come at the end of the parameter list. A parameter without a default cannot follow one with a default. Doing so gives a compile error.

At the call site, parameters with defaults can be skipped. The call CheckAge(20) on the definition static void CheckAge(int age, int limit = 18) uses the default 18 for limit.

Exercise Age limit check

Define a static void CheckAge(int age, int limit = 18) method. In the body write Console.WriteLine(age >= limit). In Main, call CheckAge(20) (use the default for limit).

Show example solution

Add Console.WriteLine(age >= limit); to the CheckAge body, write CheckAge(20); in Main.
Example solution:
using System;

class Program
{
    static void CheckAge(int age, int limit = 18)
    {
        // Print the result of age >= limit
        Console.WriteLine(age >= limit);
    }

    static void Main()
    {
        // Call CheckAge
        CheckAge(20);
    }
}

Test yourself

What does Greet() print?
```
static void Greet(string name = "Friend")
{
    Console.WriteLine("Hello, " + name);
}
Greet();
```
- Hello, Friend
- Hello,
- Hello, name
- Empty
Show answer

Hello, Friend — Correct. No argument was passed, so name = "Friend" is used.
Match each expression to its meaning

name = "Friend"

Default value
Greet()

Uses default
Greet("Ayşe")

Passes argument
static void

No return value

Default parameter

static void Greet(string name ____)
{
    Console.WriteLine(name);
}

Show answer

static void Greet(string name = "Friend")
{
    Console.WriteLine(name);
}

Next lesson: The params keyword

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