Gallery

Study Notes(Edit)

Resources

Networks

Explore

Exam Notes

Week 3: Methods and Collections

1. Methods in C#

Definition: A method is a reusable block of code designed to perform a specific task. It can accept parameters, execute code, and optionally return a value.

Syntax of a Method:

returnType MethodName(parameterList) {

// Method body

}

Example:

public int Add(int a, int b) {

return a + b;

}

Key Components of a Method:

Return Type: Specifies the type of value the method returns. If a method doesn’t return a value, use void.

Method Name: Follows PascalCase naming convention.

Parameters: Define what arguments the method takes (optional).

Return Statement: Ends the method’s execution and returns a value if specified.

Calling a Method:

int result = Add(3, 4); // Calls the Add method with arguments 3 and 4

Void Methods:

void methods do not return a value.

Example:

public void DisplayMessage() {

Console.WriteLine("Hello, World!");

}

⁠

2. Method Overloading

Definition: Method overloading allows defining multiple methods with the same name but different parameter lists.

Key Rule: Overloaded methods must differ in their parameter types, number of parameters, or both.

Example:

public int Add(int a, int b) {

return a + b;

}

public double Add(double a, double b) {

return a + b;

}

MCQ Tip: Watch out for syntax differences. Questions may include small variations, like missing parameter types or incorrect return types.

⁠

3. Parameters in Methods

Value Parameters:

By default, parameters are passed by value, meaning the method receives a copy of the argument.

Reference Parameters (ref):

Definition: Allows a method to modify the original variable by passing it by reference.

Usage: The ref keyword must be used both in the method declaration and when calling the method.

Example:

public void UpdateValue(ref int x) {

x += 10;

}

int number = 5;

UpdateValue(ref number); // number becomes 15

Out Parameters (out):

Definition: Used to return multiple values from a method. The variable must be assigned in the method before returning.

Usage: out is specified in both method definition and call.

Example:

csharp

Copy code

public void GetValues(out int a, out int b) {

a = 10;

b = 20;

}

int x, y;

GetValues(out x, out y); // x becomes 10, y becomes 20

Optional Parameters:

Allows specifying default values for parameters in the method declaration.

Example:

csharp

Copy code

public void PrintMessage(string message = "Hello") {

Console.WriteLine(message);

}

PrintMessage(); // Outputs "Hello" due to default value

⁠

4. Collections in C#

List<T>: A dynamic collection that can store elements of a specified type (T) and automatically resizes as elements are added or removed.

Key Methods and Properties:

Add: Adds an element to the end of the list.

csharp

Copy code

List<int> numbers = new List<int>();

numbers.Add(10); // Adds 10 to the list

Insert: Adds an element at a specified index, shifting other elements.

csharp

Copy code

numbers.Insert(1, 20); // Inserts 20 at index 1

Remove: Removes the first occurrence of a specified value.

csharp

Copy code

numbers.Remove(10); // Removes the first 10 from the list

Clear: Removes all elements from the list, leaving it empty.

csharp

Copy codec

numbers.Clear(); // Empties the list

Count: Retrieves the number of elements in the list.

csharp

Copy code

Console.WriteLine(numbers.Count); // Outputs the number of items

Array vs. List<T>:

Arrays have a fixed size, whereas List<T> can dynamically resize.

Lists provide more flexibility with methods like Add, Remove, and Insert.

⁠

5. Dictionary<TKey, TValue>

Definition: A collection of key-value pairs where each key is unique. Used when you need to retrieve values based on unique keys.

Key Points:

Keys must be unique, but values can be duplicated.

Commonly used methods and properties include:

Add: Adds a key-value pair.

csharp

Copy code

Dictionary<string, int> ages = new Dictionary<string, int>();

ages.Add("Alice", 25);

Remove: Removes the key-value pair with the specified key.

ContainsKey: Checks if a specific key exists.

Count: Gets the number of key-value pairs in the dictionary.

⁠

6. Common Exam MCQ Styles

Method Syntax Errors: Questions may have small syntax errors (e.g., missing return type, incorrect use of void).

Example MCQ:

Which of the following correctly defines a method with a return type of int?

(a) void Add(int x, int y) { return x + y; }

(b) int Add(int x, int y) { return x + y; } (Correct)

(d) public Add(int x, int y)

Parameters and Return Types:

Example MCQ:

What does the ref keyword do in C#?

(a) Allows a method to receive a value and make a local copy.

(b) Prevents the method from modifying the variable.

(d) Specifies that the parameter cannot be null.

List and Dictionary Operations:

Be familiar with methods like Add, Insert, Remove, Clear, and properties like Count.

Example MCQ:

Want to print your doc?
This is not the way.

Try clicking the ⋯ next to your doc name or using a keyboard shortcut (

CtrlP

) instead.