Top-level statements in modern C# - Mini Project: Build & Apply

Top-level statements in modern C#

📖 Scenario: You are creating a simple console program to greet users by name. Modern C# allows writing code without explicitly defining a class or a Main method. This makes your program shorter and easier to read.

🎯 Goal: Build a small C# program using top-level statements that asks for the user's name and then greets them with a personalized message.

📋 What You'll Learn

Use top-level statements without defining a class or Main method

Read user input from the console

Print a greeting message including the user's name

💡 Why This Matters

🌍 Real World

Top-level statements simplify small C# programs, scripts, and quick tests by removing boilerplate code.

💼 Career

Understanding top-level statements helps you write cleaner, modern C# code used in many professional projects and interviews.

1

Create a variable to store the user's name

Write a line of code to declare a variable called name and assign it the value returned by Console.ReadLine().

C Sharp (C#)

# Declare a variable called name and assign it Console.ReadLine()
# Your code here

Hint

Use string? name = Console.ReadLine(); to read input from the user.

2

Add a greeting message prefix

Create a variable called greeting and assign it the string "Hello".

C Sharp (C#)

string? name = Console.ReadLine();
# Create a variable called greeting and assign it "Hello"
# Your code here

Hint

Use string greeting = "Hello"; to store the greeting word.

3

Combine greeting and name into a message

Create a variable called message and assign it the value of $"{greeting}, {name}!" using string interpolation.

C Sharp (C#)

string? name = Console.ReadLine();
string greeting = "Hello";
# Create a variable called message using string interpolation to combine greeting and name
# Your code here

Hint

Use string message = $"{greeting}, {name}!"; to create the full greeting.

4

Print the greeting message

Write a line of code to print the message variable to the console using Console.WriteLine().

C Sharp (C#)

string? name = Console.ReadLine();
string greeting = "Hello";
string message = $"{greeting}, {name}!";
# Print the message to the console
# Your code here

Hint

Use Console.WriteLine(message); to display the greeting.

Practice

1. What is the main benefit of using top-level statements in modern C#?

easy

A. It only works for console applications with multiple classes.

B. You must always define a Main method to run the program.

C. It requires more boilerplate code than traditional C# programs.

D. You can write code without explicitly defining a class or Main method.

Solution

1. Step 1: Understand top-level statements purpose

   Top-level statements allow writing code directly without wrapping it inside a class or Main method.

2. Step 2: Compare options with this feature

   You can write code without explicitly defining a class or Main method. correctly states this benefit, while others contradict it or add incorrect restrictions.

3. Final Answer:

   You can write code without explicitly defining a class or Main method. -> Option D

4. Quick Check:

   Top-level statements remove boilerplate = A [OK]

Hint: Top-level means no class or Main method needed [OK]

Common Mistakes:

• Thinking Main method is still required
• Believing top-level statements add more code
• Assuming it only works for complex apps

2. Which of the following is the correct way to write a top-level statement program that prints "Hello, World!"?

easy

A. Console.WriteLine("Hello, World!");

B. public static void Main() { Console.WriteLine("Hello, World!"); }

C. class Program { static void Main() { Console.WriteLine("Hello, World!"); } }

D. void Main() { Console.WriteLine("Hello, World!"); }

Solution

1. Step 1: Identify top-level statement syntax

   Top-level statements allow writing code directly without class or method wrappers.

2. Step 2: Check each option

   Console.WriteLine("Hello, World!"); is direct code printing the message, valid as a top-level statement. Others require class or method definitions.

3. Final Answer:

   Console.WriteLine("Hello, World!"); -> Option A

4. Quick Check:

   Direct code without class = C [OK]

Hint: Top-level means just write code directly, no class needed [OK]

Common Mistakes:

• Adding class or Main method unnecessarily
• Using incorrect method signatures
• Forgetting to call Console.WriteLine properly

3. What will be the output of this C# program using top-level statements?

int x = 5;
int y = 10;
Console.WriteLine(x + y);

medium

A. Compilation error

B. 15

C. x + y

D. 510

Solution

1. Step 1: Understand variable initialization and addition

   Variables x and y are integers with values 5 and 10. Adding them gives 15.

2. Step 2: Check Console.WriteLine output

   Console.WriteLine prints the sum of x and y, which is 15, not concatenation or error.

3. Final Answer:

   15 -> Option B

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Adding integers prints sum, not concatenation [OK]

Common Mistakes:

• Thinking integers concatenate as strings
• Expecting variable names printed
• Assuming top-level causes errors

4. Identify the error in this top-level statement C# code:

int number = 10
Console.WriteLine(number);

medium

A. Missing semicolon after variable declaration.

B. Cannot declare variables in top-level statements.

C. Console.WriteLine is not allowed in top-level statements.

D. Variable 'number' must be declared inside a method.

Solution

1. Step 1: Check syntax of variable declaration

   The line 'int number = 10' is missing a semicolon at the end, which is required in C#.

2. Step 2: Verify top-level statement rules

   Variables can be declared and Console.WriteLine used directly in top-level statements, so other options are incorrect.

3. Final Answer:

   Missing semicolon after variable declaration. -> Option A

4. Quick Check:

   Every statement needs semicolon [OK]

Hint: Check for missing semicolons in statements [OK]

Common Mistakes:

• Thinking variables can't be declared top-level
• Assuming Console.WriteLine is disallowed
• Forgetting semicolon ends statements

5. You want to write a simple C# program using top-level statements that reads a number from the user, doubles it, and prints the result. Which code snippet correctly does this?

hard

A. class Program {
static void Main() {
Console.WriteLine("Enter a number:");
int num = int.Parse(Console.ReadLine());
Console.WriteLine(num * 2);
}
}

B. Console.WriteLine("Enter a number:");
var num = Console.ReadLine();
Console.WriteLine(num * 2);

C. Console.WriteLine("Enter a number:");
int num = int.Parse(Console.ReadLine());
Console.WriteLine(num * 2);

D. int num = Console.ReadLine();
Console.WriteLine(num * 2);

Solution

1. Step 1: Check input reading and parsing

   Console.WriteLine("Enter a number:"); int num = int.Parse(Console.ReadLine()); Console.WriteLine(num * 2); reads input as string, parses to int, then doubles it correctly.

2. Step 2: Verify top-level usage and output

   Console.WriteLine("Enter a number:"); int num = int.Parse(Console.ReadLine()); Console.WriteLine(num * 2); uses top-level statements correctly without class or Main method, and prints the doubled value.

3. Final Answer:

   Console.WriteLine("Enter a number:"); int num = int.Parse(Console.ReadLine()); Console.WriteLine(num * 2); -> Option C

4. Quick Check:

   Parse input to int before math [OK]

Hint: Parse input string to int before math [OK]

Common Mistakes:

• Not parsing input string to int
• Using class and Main when top-level allowed
• Assigning Console.ReadLine() directly to int