Array Insertion at End in DSA C# - Build from Scratch

Array Insertion at End

📖 Scenario: You are managing a list of daily temperatures recorded in a weather app. Each day, you add the new temperature at the end of the list.

🎯 Goal: Build a program that stores temperatures in an array and adds a new temperature at the end.

📋 What You'll Learn

Create an integer array called temperatures with the values 20, 22, 19, 23

Create an integer variable called newTemperature and set it to 25

Create a new array called updatedTemperatures that contains all elements of temperatures plus newTemperature at the end

Print the elements of updatedTemperatures separated by spaces

💡 Why This Matters

🌍 Real World

Adding new data points to a fixed-size array is common in systems that collect sensor data or logs where arrays are used for storage.

💼 Career

Understanding how to manually resize arrays and insert elements is fundamental for programming in languages like C# where arrays have fixed size, and it builds a foundation for learning dynamic data structures.

1

Create the initial array

Create an integer array called temperatures with these exact values: 20, 22, 19, 23

DSA C#

# Your code here

Hint

Use int[] temperatures = {20, 22, 19, 23}; to create the array.

2

Add the new temperature variable

Create an integer variable called newTemperature and set it to 25

DSA C#

int[] temperatures = {20, 22, 19, 23};
# Your code here

Hint

Use int newTemperature = 25; to create the variable.

3

Create the updated array with the new temperature at the end

Create a new integer array called updatedTemperatures that contains all elements of temperatures plus newTemperature at the end

DSA C#

int[] temperatures = {20, 22, 19, 23};
int newTemperature = 25;
# Your code here

Hint

Create a new array with size one more than temperatures. Copy all elements, then add newTemperature at the last index.

4

Print the updated array

Print all elements of updatedTemperatures separated by spaces using a for loop

DSA C#

int[] temperatures = {20, 22, 19, 23};
int newTemperature = 25;
int[] updatedTemperatures = new int[temperatures.Length + 1];
for (int i = 0; i < temperatures.Length; i++)
{
    updatedTemperatures[i] = temperatures[i];
}
updatedTemperatures[updatedTemperatures.Length - 1] = newTemperature;

# Your code here

Hint

Use a for loop to print each element followed by a space.

Practice

1. What happens when you insert an element at the end of a fixed-size array in C# without resizing?

easy

A. An error occurs because the array size is fixed

B. The array automatically resizes to fit the new element

C. The element replaces the last element if the array is full

D. The element is added at the first position

Solution

1. Step 1: Understand fixed-size array behavior

   In C#, arrays have a fixed size once created and cannot grow automatically.

2. Step 2: Inserting at the end without resizing

   Inserting at the end requires accessing index arr.Length, which is out of bounds and throws IndexOutOfRangeException.

3. Final Answer:

   An error occurs because the array size is fixed -> Option A

4. Quick Check:

   Fixed-size array insert at end causes error [OK]

Hint: Fixed arrays can't grow; insert at end causes error [OK]

Common Mistakes:

• Assuming array resizes automatically
• Thinking insertion shifts elements
• Believing insertion adds new slot

2. Which of the following is the correct syntax to insert an element at the end of a List<int> named numbers in C#?

easy

A. numbers.Push(5);

B. numbers.InsertEnd(5);

C. numbers.Add(5);

D. numbers.Append(5);

Solution

1. Step 1: Identify List insertion method

   In C#, List<T> uses the Add() method to insert elements at the end.

2. Step 2: Check other options

   InsertEnd, Push, and Append are not valid List<T> methods in C#.

3. Final Answer:

   numbers.Add(5); -> Option C

4. Quick Check:

   List Add method inserts at end [OK]

Hint: Use Add() to insert at end of List [OK]

Common Mistakes:

• Using non-existent methods like InsertEnd or Push
• Confusing List with Stack methods
• Trying Append which is for strings

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

int[] arr = new int[3] {1, 2, 3};
arr[2] = 10;
Console.WriteLine(string.Join(", ", arr));

medium

A. 1, 2, 3

B. 1, 2, 10

C. 10, 2, 3

D. Runtime error

Solution

1. Step 1: Understand array initialization

   The array arr has 3 elements: 1, 2, 3 at indexes 0, 1, 2.

2. Step 2: Assign new value at last index

   arr[2] = 10 replaces the last element (3) with 10.

3. Final Answer:

   1, 2, 10 -> Option B

4. Quick Check:

   Last element replaced with 10 [OK]

Hint: Index 2 is last element; assignment replaces it [OK]

Common Mistakes:

• Thinking array resizes or shifts elements
• Expecting original array unchanged
• Assuming runtime error on assignment

4. Identify the error in the following code that tries to insert 7 at the end of an array:

int[] arr = new int[3] {1, 2, 3};
arr[arr.Length] = 7;

medium

A. Syntax error due to missing semicolon

B. Null reference exception

C. No error, code runs fine

D. Index out of range error

Solution

1. Step 1: Check array index used

   arr.Length is 3, but valid indexes are 0,1,2 only.

2. Step 2: Understand index out of range

   Accessing arr[3] causes an IndexOutOfRangeException at runtime.

3. Final Answer:

   Index out of range error -> Option D

4. Quick Check:

   Array index must be less than length [OK]

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

Common Mistakes:

• Using arr.Length as index directly
• Ignoring runtime exceptions
• Confusing syntax errors with runtime errors

5. You have an array int[] arr = new int[3] {1, 2, 3};. You want to insert 4 at the end without losing existing elements. Which approach is correct?

hard

A. Create a new array of size 4, copy old elements, then add 4 at last index

B. Assign arr[3] = 4 directly

C. Use arr.Add(4) method

D. Resize arr using arr.Resize(4) method

Solution

1. Step 1: Understand fixed array size

   Arrays in C# have fixed size; cannot add elements beyond initial size.

2. Step 2: Correct way to add element

   Create a new larger array, copy existing elements, then insert new element at the end.

3. Step 3: Check other options

   Assigning arr[3] causes error; arr.Add() doesn't exist for arrays; arr.Resize() is invalid.

4. Final Answer:

   Create a new array of size 4, copy old elements, then add 4 at last index -> Option A

5. Quick Check:

   Fixed arrays need new array to grow [OK]

Hint: Arrays fixed size; create new bigger array to add [OK]

Common Mistakes:

• Trying to assign beyond array length
• Using List methods on arrays
• Assuming Resize method exists