What is C# - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary use of C#?

C# is a programming language. What is it mainly used for?

A Building Windows desktop applications and web services

B Creating databases and managing data with SQL

C Designing website layouts with HTML and CSS

D Writing scripts for Linux shell commands

💡 Hint

Think about what kind of programs you can build with C# on Windows.

C# is mainly used to build Windows desktop apps, web services, and games using frameworks like .NET.

❓ Predict Output

intermediate

What is the output of this C# code?

Look at this C# program. What will it print?

C Sharp (C#)

using System;
class Program {
  static void Main() {
    int x = 5;
    int y = 3;
    Console.WriteLine(x + y);
  }
}

A 5 + 3

B 53

C Error: Cannot add integers

D 8

💡 Hint

Adding two numbers returns their sum.

The program adds 5 and 3, printing 8.

🔧 Debug

advanced

What error does this C# code produce?

What error will this code cause when run?

C Sharp (C#)

using System;
class Program {
  static void Main() {
    int number = "10";
    Console.WriteLine(number);
  }
}

A Output: 10

B Runtime error: NullReferenceException

C Compile-time error: Cannot convert string to int

D Compile-time error: Missing semicolon

💡 Hint

Check the type assigned to an integer variable.

You cannot assign a string value to an int variable in C# without conversion.

📝 Syntax

advanced

Which option correctly declares a method in C#?

Choose the correct way to declare a method that returns an integer and takes no parameters.

A int GetNumber() { return 5; }

B GetNumber() int { return 5; }

C int GetNumber { return 5; }

D int GetNumber() => { 5; }

💡 Hint

Remember the order: return type, method name, parentheses, braces.

Option A follows correct C# syntax for method declaration.

🚀 Application

expert

What is the value of 'result' after running this C# code?

Consider this code snippet. What is the value of result after execution?

C Sharp (C#)

using System;
class Program {
  static int Multiply(int a, int b = 2) {
    return a * b;
  }
  static void Main() {
    int result = Multiply(3);
    Console.WriteLine(result);
  }
}

A 3

B 6

C 5

D Error: Missing argument for parameter 'b'

💡 Hint

Check the default value of parameter b.

The method Multiply uses default value 2 for b, so 3 * 2 = 6.

Practice

1. What is C# primarily used for?

easy

A. Creating animations and graphics only

B. Designing websites with HTML and CSS

C. Building software applications, especially on Windows

D. Managing databases with SQL

Solution

1. Step 1: Understand C# usage

   C# is a programming language used to build software applications.

2. Step 2: Identify platform focus

   C# is especially popular for Windows software development.

3. Final Answer:

   Building software applications, especially on Windows -> Option C

4. Quick Check:

   C# = Windows software language [OK]

Hint: Remember C# is mainly for Windows apps [OK]

Common Mistakes:

• Confusing C# with web design languages
• Thinking C# is only for databases
• Believing C# is just for graphics

2. Which of the following is the correct way to start a C# program?

easy

A. void Start() {}

B. static void Main(string[] args) {}

C. function main() {}

D. begin main() {}

Solution

1. Step 1: Identify C# program entry point

   The Main method is the standard starting point in C# programs.

2. Step 2: Check syntax correctness

   Only static void Main(string[] args) {} uses correct C# syntax with static void Main and string[] args.

3. Final Answer:

   static void Main(string[] args) {} -> Option B

4. Quick Check:

   Main method syntax = static void Main(string[] args) {} [OK]

Hint: Look for 'static void Main' to find C# entry point [OK]

Common Mistakes:

• Using JavaScript or other language syntax
• Missing 'static' keyword in Main method
• Using lowercase 'main' instead of 'Main'

3. What will the following C# code output?

using System;
class Program {
  static void Main() {
    Console.WriteLine("Hello, C#");
  }
}

medium

A. Error: Missing Main method

B. Hello C#

C. Console.WriteLine("Hello, C#");

D. Hello, C#

Solution

1. Step 1: Analyze the code output command

   The code calls Console.WriteLine with the string "Hello, C#" which prints it exactly.

2. Step 2: Confirm program runs without errors

   The Main method is correct and will print the string to the console.

3. Final Answer:

   Hello, C# -> Option D

4. Quick Check:

   Console.WriteLine prints text = Hello, C# [OK]

Hint: Console.WriteLine prints exactly what is inside quotes [OK]

Common Mistakes:

• Ignoring the comma in the output
• Thinking code prints the code line itself
• Assuming syntax error due to special characters

4. Identify the error in this C# program:

using System;
class Program {
  void Main() {
    Console.WriteLine("Hi");
  }
}

medium

A. Main method must be static

B. Console.WriteLine is misspelled

C. Missing semicolon after class declaration

D. Class name must be lowercase

Solution

1. Step 1: Check Main method declaration

   Main method must be static to run as program entry point in C#.

2. Step 2: Verify other syntax elements

   Console.WriteLine is correct, semicolons after class are not needed, class names can be uppercase.

3. Final Answer:

   Main method must be static -> Option A

4. Quick Check:

   Main method static keyword required [OK]

Hint: Main method must have 'static' keyword [OK]

Common Mistakes:

• Forgetting 'static' on Main method
• Thinking class names must be lowercase
• Assuming Console.WriteLine is incorrect

5. You want to create a simple C# program that prints "Welcome!" when run. Which of these is the best complete program?

hard

A. using System;
class Program { static void Main() { Console.WriteLine("Welcome!"); } }

B. static void Main() { Console.WriteLine("Welcome!"); }

C. class Program { void Main() { print("Welcome!"); } }

D. function Main() { Console.WriteLine("Welcome!"); }

Solution

1. Step 1: Check for complete program structure

   using System; class Program { static void Main() { Console.WriteLine("Welcome!"); } } has a class named Program and a static Main method, which is required.

2. Step 2: Verify correct output command and syntax

   Console.WriteLine is correct for printing, and the string is properly quoted.

3. Final Answer:

   using System; class Program { static void Main() { Console.WriteLine("Welcome!"); } } -> Option A

4. Quick Check:

   Complete C# program = using System; class Program { static void Main() { Console.WriteLine("Welcome!"); } } [OK]

Hint: Complete C# program needs class and static Main [OK]

Common Mistakes:

• Omitting class wrapper
• Missing static keyword on Main
• Using wrong print function