Single-dimensional array declaration in C Sharp (C#)

Introduction

Arrays help you store many values of the same type in one place. A single-dimensional array is like a row of boxes where each box holds one value.

When you want to keep a list of numbers, like scores in a game.

When you need to store names of students in a class.

When you want to hold daily temperatures for a week.

When you want to process a fixed number of items one by one.

When you want to loop through a collection of items easily.

Syntax

C Sharp (C#)

public class SingleDimensionalArrayExample
{
    public static void Main()
    {
        // Declare an array of integers with 5 elements
        int[] numbers = new int[5];

        // Declare and initialize an array of strings
        string[] names = { "Alice", "Bob", "Charlie" };
    }
}

The number inside the square brackets [] defines the size of the array.

You can declare and initialize an array at the same time or separately.

Examples

This creates an empty array with zero elements.

C Sharp (C#)

int[] emptyArray = new int[0];

An array with one element. You can assign a value to the first (and only) box.

C Sharp (C#)

int[] singleElementArray = new int[1];
singleElementArray[0] = 42;

Declare and fill the array with 3 fruit names right away.

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry" };

Assign values to the first and last elements in a 5-element array.

C Sharp (C#)

int[] numbers = new int[5];
numbers[0] = 10;
numbers[4] = 50;

Sample Program

This program shows how to declare a single-dimensional array, print its default values, assign new values, and print them again.

C Sharp (C#)

using System;

public class SingleDimensionalArrayExample
{
    public static void Main()
    {
        // Declare and initialize an array of 5 integers
        int[] scores = new int[5];

        Console.WriteLine("Scores before assignment:");
        for (int index = 0; index < scores.Length; index++)
        {
            Console.WriteLine($"scores[{index}] = {scores[index]}");
        }

        // Assign values to the array
        scores[0] = 85;
        scores[1] = 90;
        scores[2] = 78;
        scores[3] = 92;
        scores[4] = 88;

        Console.WriteLine("\nScores after assignment:");
        for (int index = 0; index < scores.Length; index++)
        {
            Console.WriteLine($"scores[{index}] = {scores[index]}");
        }
    }
}

Important Notes

Time complexity to access or assign an element by index is O(1) - very fast.

Space complexity is proportional to the number of elements you declare.

Common mistake: Accessing an index outside the array size causes an error.

Use arrays when you know the number of elements in advance and want fast access by position.

Summary

Single-dimensional arrays store multiple values of the same type in a simple list.

You declare them by specifying the type, square brackets, and size or initial values.

Access elements by their position using zero-based indexes.

Practice

1. Which of the following correctly declares a single-dimensional array of integers in C#?

easy

A. int[] numbers = new int[5];

B. int numbers = new int[5];

C. int[] numbers = int[5];

D. int numbers[] = new int();

Solution

1. Step 1: Understand array declaration syntax

   In C#, a single-dimensional array is declared by specifying the type followed by square brackets and then initializing with 'new' and size.

2. Step 2: Check each option

   int[] numbers = new int[5]; correctly uses 'int[] numbers = new int[5];'. Others have syntax errors or wrong types.

3. Final Answer:

   int[] numbers = new int[5]; -> Option A

4. Quick Check:

   Correct array declaration = int[] numbers = new int[5]; [OK]

Hint: Remember: type[] name = new type[size]; for arrays [OK]

Common Mistakes:

• Forgetting square brackets after type
• Not using 'new' keyword
• Declaring array without size or initializer

2. Which of the following is the correct syntax to declare and initialize a single-dimensional string array with 3 elements in C#?

easy

A. string[] names = new string[2] {"Anna", "Bob", "Cara"};

B. string names[] = {"Anna", "Bob", "Cara"};

C. string[] names = new string {"Anna", "Bob", "Cara"};

D. string[] names = new string[] {"Anna", "Bob", "Cara"};

Solution

1. Step 1: Understand array initialization syntax

   In C#, you can initialize an array with values using 'new type[] { values }' or just '{ values }' if declaration and initialization are combined.

2. Step 2: Check each option

   string[] names = new string[] {"Anna", "Bob", "Cara"}; is fully correct. string[] names = new string[2] {"Anna", "Bob", "Cara"}; incorrectly specifies size 2 with 3 initializers (compile error). string names[] = {"Anna", "Bob", "Cara"}; uses invalid syntax. string[] names = new string {"Anna", "Bob", "Cara"}; invalid syntax (missing array dimensions).

3. Final Answer:

   string[] names = new string[] {"Anna", "Bob", "Cara"}; -> Option D

4. Quick Check:

   Explicit array init with new string[] = string[] names = new string[] {"Anna", "Bob", "Cara"}; [OK]

Hint: Use 'new type[] { ... }' for explicit array initialization [OK]

Common Mistakes:

• Specifying size with initializer list
• Using C-style array syntax
• Omitting 'new' keyword incorrectly

3. What will be the output of the following C# code?

int[] arr = new int[3] {10, 20, 30};
Console.WriteLine(arr[1]);

medium

A. 20

B. 10

C. 30

D. Runtime error

Solution

1. Step 1: Understand array indexing

   Arrays in C# are zero-based, so arr[0] = 10, arr[1] = 20, arr[2] = 30.

2. Step 2: Identify the printed element

   The code prints arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember arrays start at index 0 in C# [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Expecting output to be 10 or 30
• Thinking array indexes start at 1

4. Identify the error in the following C# code snippet:

int[] values;
values = new int[3];
values[3] = 100;

medium

A. Array size is not specified

B. Index out of range error

C. Missing array initialization

D. Syntax error in declaration

Solution

1. Step 1: Check array size and indexing

   The array 'values' is declared with size 3, so valid indexes are 0, 1, and 2.

2. Step 2: Analyze the assignment

   Assigning to values[3] is invalid and causes an IndexOutOfRangeException at runtime.

3. Final Answer:

   Index out of range error -> Option B

4. Quick Check:

   Accessing index 3 in size 3 array causes error [OK]

Hint: Array indexes go from 0 to size-1 only [OK]

Common Mistakes:

• Using index equal to array size
• Forgetting zero-based indexing
• Assuming array auto-expands

5. You want to declare a single-dimensional array of 4 doubles and initialize it with values 1.1, 2.2, 3.3, and 4.4. Which code snippet correctly does this and allows you to change the third element later?

hard

A. double[] data = new double[3] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5;

B. double[] data = new double[3]; data[2] = 5.5;

C. double[] data = new double[4] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5;

D. double data[] = new double[] {1.1, 2.2, 3.3, 4.4}; data[3] = 5.5;

Solution

1. Step 1: Check array declaration and initialization

   double[] data = new double[4] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5; declares an array of size 4 with initial values and allows modification of elements.

2. Step 2: Verify element modification

   double[] data = new double[3] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5; incorrectly specifies size 3 with 4 initializers (compile error). double data[] = new double[] {1.1, 2.2, 3.3, 4.4}; data[3] = 5.5; uses invalid syntax but index 3 is valid for size 4 array. double[] data = new double[3]; data[2] = 5.5; declares size 3, not 4, missing initialization.

3. Final Answer:

   double[] data = new double[4] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5; -> Option C

4. Quick Check:

   Explicit size and initializer with modifiable element = double[] data = new double[4] {1.1, 2.2, 3.3, 4.4}; data[2] = 5.5; [OK]

Hint: Use 'new type[size] {values}' to declare and initialize arrays [OK]

Common Mistakes:

• Mismatching array size and initializer count
• Using wrong index for element change
• Omitting 'new' keyword in some contexts