Single-dimensional array declaration in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a single-dimensional array in C#?

A single-dimensional array in C# is a collection of elements of the same type stored in a linear sequence. It is like a row of boxes where each box holds one value.

beginner

How do you declare a single-dimensional array of integers with 5 elements in C#?

You declare it like this:
int[] numbers = new int[5];
This creates an array named 'numbers' that can hold 5 integers.

beginner

What does the number inside the square brackets mean in new int[5]?

It means the size of the array, or how many elements it can hold. Here, the array can hold 5 integers.

beginner

How can you initialize a single-dimensional array with values at the time of declaration?

You can write:
int[] numbers = {1, 2, 3, 4, 5};
This creates an array with 5 elements and sets their values immediately.

beginner

What is the index of the first element in a C# array?

The first element's index is 0. Arrays in C# are zero-based, so counting starts from 0.

How do you declare a single-dimensional array of strings named 'names' with 3 elements in C#?

A string[] names = new string[3];

B string names = new string[3];

C string[] names = string[3];

D string names[] = new string(3);

Option A correctly declares a string array with 3 elements. The others have syntax errors.

What is the index of the last element in an array declared as int[] arr = new int[10];?

A 1

B 9

C 0

D 10

Since indexing starts at 0, the last element is at index 9 for an array of size 10.

Which of the following initializes an array with values 10, 20, 30 in C#?

A int[] nums = new int[3] {10, 20, 30};

B int nums[] = new int{10, 20, 30};

C int[] nums = {10, 20, 30};

D int nums = new int[3] {10, 20, 30};

Options A and C correctly declare and initialize the array with the given values. The others have syntax errors.

What happens if you try to access an array element with an index outside its range?

A The program ignores the request.

B It returns null.

C It returns the last element.

D You get a runtime error called IndexOutOfRangeException.

Accessing outside the array bounds causes a runtime error in C#.

Which keyword is used to create a new array instance in C#?

A new

B create

C array

D init

The 'new' keyword is used to create new array instances.

Explain how to declare and initialize a single-dimensional array of integers with 4 elements in C#.

Think about the syntax: type[], name, new, size or values.

Describe what zero-based indexing means in the context of C# arrays.

Imagine counting boxes starting at zero.

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