Array indexing and access in C Sharp (C#) - Mini Project: Build & Apply

Array Indexing and Access in C#

📖 Scenario: You are working on a simple program that stores the names of fruits in an array. You want to access specific fruits by their position in the array.

🎯 Goal: Build a C# program that creates an array of fruits, sets an index variable, accesses the fruit at that index, and prints it.

📋 What You'll Learn

Create an array called fruits with these exact values: "Apple", "Banana", "Cherry", "Date", "Elderberry"

Create an integer variable called index and set it to 2

Access the fruit at position index in the fruits array and store it in a variable called selectedFruit

Print the value of selectedFruit exactly

💡 Why This Matters

🌍 Real World

Arrays are used to store lists of items like names, prices, or dates. Accessing items by index helps you get or change specific data quickly.

💼 Career

Knowing how to work with arrays and access their elements is a basic skill for many programming jobs, including software development and data processing.

1

Create the fruits array

Create a string array called fruits with these exact values: "Apple", "Banana", "Cherry", "Date", "Elderberry"

C Sharp (C#)

// Your code here

Hint

Use string[] fruits = { ... }; to create the array with the exact fruit names.

2

Set the index variable

Create an integer variable called index and set it to 2

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };
// Your code here

Hint

Use int index = 2; to create the index variable.

3

Access the fruit at the index

Create a string variable called selectedFruit and set it to the fruit at position index in the fruits array

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };
int index = 2;
// Your code here

Hint

Use string selectedFruit = fruits[index]; to get the fruit at the given index.

4

Print the selected fruit

Write a Console.WriteLine statement to print the value of selectedFruit

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };
int index = 2;
string selectedFruit = fruits[index];
// Your code here

Hint

Use Console.WriteLine(selectedFruit); to print the fruit.

Practice

1. What is the index of the first element in a C# array int[] numbers = {10, 20, 30};?

easy

A. 0

B. 1

C. 10

D. Array length - 1

Solution

1. Step 1: Understand zero-based indexing in C# arrays

   Arrays in C# start counting indexes from 0, so the first element is at index 0.

2. Step 2: Identify the first element's index

   The first element 10 is at index 0, not 1 or any other number.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   First element index = 0 [OK]

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

Common Mistakes:

• Thinking the first index is 1
• Confusing element value with index
• Using array length as first index

2. Which of the following is the correct way to access the third element of an array string[] fruits = {"apple", "banana", "cherry"};?

easy

A. fruits[2]

B. fruits[3]

C. fruits(2)

D. fruits{2}

Solution

1. Step 1: Recall C# array indexing syntax

   Arrays use square brackets [] to access elements by zero-based index.

2. Step 2: Identify the correct index for the third element

   The third element is at index 2, so fruits[2] is correct.

3. Final Answer:

   fruits[2] -> Option A

4. Quick Check:

   Third element index = 2 [OK]

Hint: Use square brackets and zero-based index [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using curly braces instead of brackets
• Using index 3 for third element

3. What will be the output of this code?

int[] values = {5, 10, 15};
Console.WriteLine(values[1]);

medium

A. 5

B. Runtime error

C. 10

D. 15

Solution

1. Step 1: Identify the element at index 1

   The array values has elements 5 at index 0, 10 at index 1, and 15 at index 2.

2. Step 2: Determine the output of Console.WriteLine(values[1])

   Accessing values[1] prints 10 to the console.

3. Final Answer:

   10 -> Option C

4. Quick Check:

   values[1] = 10 [OK]

Hint: Index 1 means second element in array [OK]

Common Mistakes:

• Printing values[0] instead of values[1]
• Confusing index with element value
• Expecting index to start at 1

4. What is wrong with this code?

int[] arr = {1, 2, 3};
Console.WriteLine(arr[3]);

medium

A. No error, prints 3

B. Index out of range runtime error

C. Syntax error due to missing semicolon

D. Prints 0 by default

Solution

1. Step 1: Check array size and valid indexes

   The array has 3 elements with indexes 0, 1, and 2. Index 3 is outside the array bounds.

2. Step 2: Understand what happens when accessing invalid index

   Accessing arr[3] causes a runtime error: IndexOutOfRangeException.

3. Final Answer:

   Index out of range runtime error -> Option B

4. Quick Check:

   Accessing invalid index causes runtime error [OK]

Hint: Index must be less than array length [OK]

Common Mistakes:

• Assuming index 3 is valid for 3-element array
• Expecting default zero value for invalid index
• Confusing syntax error with runtime error

5. Given int[] data = {2, 4, 6, 8, 10};, which expression correctly changes the last element to 20?

hard

A. data[5] = 20;

B. data[data.Length] = 20;

C. data[-1] = 20;

D. data[4] = 20;

Solution

1. Step 1: Identify the last index of the array

   The array has 5 elements, so indexes go from 0 to 4. The last element is at index 4.

2. Step 2: Choose the correct syntax to assign new value

   Assigning data[4] = 20; changes the last element to 20. Using data.Length or negative indexes is invalid.

3. Final Answer:

   data[4] = 20; -> Option D

4. Quick Check:

   Last index = Length - 1 = 4 [OK]

Hint: Last index = Length - 1 for assignment [OK]

Common Mistakes:

• Using data.Length as index (out of range)
• Using negative index (not supported)
• Using index equal to array size