C# 04: Data Structures

How to use arrays, collections and structures in C#.

Overview

Reference types differ from the value types previously discussed.

• Value types are initilised with one-part syntax {type} {variableName};, where the variable name points to a chunk of memory.
• Reference types are initialised with two-part syntax {ClassName} {variableName} = new {ClassName}();, where the variable name references an object, and the new operator creates an object in memory and returns a reference to that object.

Arrays

Arrays are reference type objects. They are indicated with square brackets.

Indexing:

• elements can be accessed with the index number, beginning at zero.

Properties:

• .Length returns the number of elements in the array.

Consider this longform example which creates an array to hold 6 integers:

// Initialise a variable of array type & Instantiate an array object associated it the variable
int[] numbers = new int[6];

double[] prices = new double[301];
decimal[] amounts = new decimal[25];
string[] names = new string[1500]

Once an array variable has been created, you can access its elements by index number, starting at zero:

const int MEDALS = 3;
string[] medallion = new string[MEDALS]; 

// Set values by index position 
medallion[0] = "Gold";
medallion[1] = "Silver";
medallion[2] = "Bronze";

The .Length property returns the number of elements in the array and can be used to loop through the array:

double price; 
double[] prices = new double[25];

for (int index = 0; index < prices.Length; index ++)
{
    price = prices[index];
}

foreach loop over array

If you just need to loop through every item in an array (i.e. without filtering criteria),

double[] prices = new double[25];

foreach (int val in numbers)
{
    // Display in Message Box 
    ShowArray(var); 
}

Two-Dimensional Arays

A two-dimensional array is indicated with a comma inside the square brackets [,] and requires row and column parameters:

int rows = 2;
int cols = 3; 

int[,] items = new int[rows, cols];

The two-dimensional array has matching indexing matching rows and columns, e.g. items[1, 2].

Use nested loops to iterate through all the row and column elements:

const int SEARCH_ROWS = 2;
const int SEARCH_COLS = 3; 

int total = 0; // accumulator

// implicit sizing and initialization
int[,] items = {
    {0, 1, 2, 3}, 
    {4, 5, 6, 7},
    {8, 9, 10, 11} };

// sum the elements
for (int row = 0; row < SEARCH_ROWS; row++)
{
    for(int col = 0; col < SEARCH_COLS, col++)
    {
        total += items[row, col];
    }
}

// display the total
MessageBox.Show(total.ToString("c"));

Lists

A list object automatically adjusts its size so you don’t need to know how many elements you need to handle.

The list declaration syntax uses angle brackets: List<{type}> {variableName} = new List<{type}>();.

To initialise the list:

List<int> myList = new List<int>() {1, 2, 3};

Indexing:

• items can be accessed with the index number, beginning at zero.

Properties:

• .Count returns the number of items in the list.
• .RemoveAt() return success or failure in deleting an item at the given index position.
• .Clear() truncates the list.
• ,IndexOf() returns the index position of a search term, with optional start and end positions.

Structures

Structures are declared by field:

// Instantiate a Structure 
struct myVehicle
{
    public string make;
    public int year;
    public double mileage;
}

// Assign Values
myVehicle.make = "Ford Fiesta";

Listing Structures

// Instantiate a structure object implicitly
Automobile sportsCar = new Automobile();

// Instantiate using `object initializer syntax`
Automobile truck = new Automobile() {
    make = "Dodge Ram",
    year = 1984,
    mileage = 9964.33};

// Store in list
List<Automobile> vehicles = New List<Automobile>();

// Add to list
vehicles.Add(sportsCar); 
vehicles.Add(truck);

Enumerators

Note that these are constants, not strings.

enum moonPhase = {Waxing, Waning}; 

// declare a variable of that type
moonPhase mPhase;

// Assign a value to the variable
mPhase = moonPhase.Waking; 

// Get integer value (defaults to index)
int idx = int(moonPhase);

Dictionaries

Access the dictionary class by using Systesm.Collection.Generics;.

Instantiate a dictionary with the syntax Dictionary<KeyType, ValueType> dictName = new Dictionary<KeyType, ValueType>();.

For example:

Dictionary<int, string> customers = new Dictionary<int, string>() 
{
    {1, "Abermarle"}, 
    {2, "Beatrice"},
    {3, "Charleswood"}
};

or:

Dictionary<int, string> customers = new Dictionary<int, string>(); 
customers[1] = "Abermarle"; 
customers[2] = "Beatrice";
customers[3] = "Charleswood";

Methods

• .Add()
• .Remove()
• .ContainsKey()
• .ContainsValue()
• .Contains(KeyValuePair)
• .TryGetValue(Key, out myVariable)
• .Count
• .ElementAt(i)
• .Clear()

QED

© Adam Heinz

6 November 2024