C# Methods

1. Defining methods

The basic syntax for defining a method in C# is as follows:

<access modifier> <return type> <method name>(<parameter list>)
{
    method body
}

A method consists of the following elements:

• Access modifiers(Access Modifier): Controls the visibility of the method, such aspublic、private、protected、internal。
• Return Type(Return Type): The data type of the method's return value. If the method does not return any value, usevoid。
• method name(Method Name): The unique identifier of the method, following PascalCase naming conventions (e.g.FindMax、GetUserName）。
• Parameter list(Parameter List): The inputs that the method receives, enclosed in parentheses. Parameters are optional; a method can have no parameters.
• method body(Method Body): Contains the code that implements the functionality, enclosed in curly braces{}Surround.

The following figure shows the complete structure of a method:

1.1 First method example

The following defines aFindMaxA method that takes two integers and returns the larger one:

The method invocation process:

Cross-class call:As long as the method is declared aspublic, then it can be called from other classes by creating an instance. This is the foundation of code reuse in object-oriented programming.

2. Parameter passing methods

C# provides three ways to pass parameters to methods. Their core difference lies inWhether to share memory：

2.1 Passing by value (default)

Passing by value is the default. The value of the argument will beCopygiven to the parameter; modifications to the parameter inside the method will not affect the original variable:

调用前：a=100, b=200
  方法内：x=200, y=100
调用后：a=100, b=200

2.2 Passing by reference (ref)

UsagerefThe keyword passes the variable'sReference(memory address); modifications to the parameter inside the method will directly affect the original variable. Note that the keyword must also be added when calling.ref：

调用前：a=100, b=200
调用后：a=200, b=100

The difference between ref and out:refRequires the variable before passingMust be already initialized；outThen it is not required, but inside the methodThe out parameter must be assigned a valuebefore it can be used.

2.3 Output parameters (out)

outParameters allow the method toReturn multiple values. AndrefThe difference is that the variable does not need to be initialized before the call, but the method must assign a value to it:

Since C# 7.0, you can, when calling,Inline declarationout variables make the code more concise:

// C# 7.0+ 内联声明
if (int.TryParse("123", out int number))
    Console.WriteLine($"解析成功：{number}");

3. Recursive methods

Recursion refers to a methodCall itselfEach recursive method requires two elements:

• Base condition(Base Case): The condition that terminates recursion, preventing infinite recursion.
• Recursive step(Recursive Step): Decomposes the problem into smaller subproblems.

Classic example — calculating factorial $$n! = n \times (n-1)!$$:

6! = 720
7! = 5040
8! = 40320

The expansion process of recursive calls:

Factorial(4)
  = 4 × Factorial(3)
  = 4 × 3 × Factorial(2)
  = 4 × 3 × 2 × Factorial(1)
  = 4 × 3 × 2 × 1
  = 24

Note:When recursion depth is too large, it may causeStackOverflowExceptionFor performance-sensitive scenarios, consider using a loop instead.

4. More features of methods

4.1 Default parameters and named parameters

C# allows parameters to be set withDefault valueyou can omit these parameters when calling. Combined withNamed parametersyou can also skip some parameters and only specify the ones that follow:

4.2 Expression-bodied methods

When the method body has only one statement, you can use=>Simplified syntax (C# 6.0+):

// 传统写法
public int Add(int a, int b)
{
    return a + b;
}

// 表达式体写法（等价）
public int Add(int a, int b) => a + b;

4.3 Method Overloading (Overloading)

In the same class, there can beMultiple methods with the same nameas long as the parameter lists are different (different parameter types, counts, or order):

Summary