Main method as entry point in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# program?

Consider this C# program with a Main method. What will it print when run?

C Sharp (C#)

using System;
class Program {
    static void Main(string[] args) {
        Console.WriteLine("Hello from Main!");
    }
}

A Hello from Main!

B No output, program compiles but does nothing

C Compilation error: Main method missing return type

D Runtime error: Main method not found

💡 Hint

The Main method is the entry point and runs automatically.

The Main method is the starting point of a C# console application. It runs and prints the string to the console.

❓ Predict Output

intermediate

What happens if Main method has wrong signature?

What will happen if the Main method is declared without static keyword in C#?

C Sharp (C#)

using System;
class Program {
    void Main(string[] args) {
        Console.WriteLine("Hello");
    }
}

A Program compiles but does nothing

B Program runs and prints Hello

C Runtime error: Main method not found

D Compilation error: Main method must be static

💡 Hint

Main method must be static because it is called by runtime without an instance.

In C#, the Main method must be static because the runtime calls it without creating an object instance. Omitting static causes a compile-time error.

❓ Predict Output

advanced

What is the output of this overloaded Main method program?

This program has two Main methods. What will it print when run?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        Console.WriteLine("Main without args");
    }
    static void Main(string[] args) {
        Console.WriteLine("Main with args");
    }
}

A Main with args

B Main without args

C Compilation error: duplicate Main methods

D Runtime error: ambiguous entry point

💡 Hint

When running from command line, Main with string[] args is called by default.

The C# runtime calls the Main method with string[] args if it exists. So it prints "Main with args".

🧠 Conceptual

advanced

Which Main method signature is valid as entry point?

Select the only valid Main method signature that can be used as the entry point in a C# console application.

A static int Main()

B public static void Main(string[] args)

C void Main()

D public void Main(string args)

💡 Hint

Main must be static and can have string[] args parameter.

Valid Main signatures include static void Main(string[] args) or static int Main(). The method must be static and have correct parameter types.

❓ Predict Output

expert

What is the output of this program with async Main?

This program uses async Main method. What will it print when run?

C Sharp (C#)

using System;
using System.Threading.Tasks;
class Program {
    static async Task Main() {
        await Task.Delay(100);
        Console.WriteLine("Async Main finished");
    }
}

A Runtime error: Task not awaited

B Compilation error: async Main not supported

C Async Main finished

D No output, program exits immediately

💡 Hint

Modern C# supports async Main returning Task.

Since C# 7.1, async Main returning Task is supported. The program waits 100ms then prints the message.

Practice

1.

What is the role of the Main method in a C# program?

easy

A. It is the entry point where program execution starts.

B. It defines global variables for the program.

C. It handles exceptions automatically.

D. It compiles the program into an executable.

Solution

1. Step 1: Understand program execution flow

   The Main method is the first method called when a C# program runs.

2. Step 2: Identify the role of Main

   It acts as the starting point, controlling program flow from the beginning.

3. Final Answer:

   It is the entry point where program execution starts. -> Option A

4. Quick Check:

   Main method = program start [OK]

Hint: Main method is where the program begins running [OK]

Common Mistakes:

• Thinking Main defines variables globally
• Confusing Main with exception handling
• Believing Main compiles the program

2.

Which of the following is the correct signature for the Main method in C#?

easy

A. static void main(string args)

B. void Main(string[] args) static

C. public void Main()

D. public static void Main(string[] args)

Solution

1. Step 1: Check method modifiers and parameters

   Main must be static and can be public. It accepts a string array parameter for arguments.

2. Step 2: Validate syntax correctness

   public static void Main(string[] args) matches the correct signature: public static void Main(string[] args).

3. Final Answer:

   public static void Main(string[] args) -> Option D

4. Quick Check:

   Correct Main signature = public static void Main(string[] args) [OK]

Hint: Main must be static and accept string array args [OK]

Common Mistakes:

• Using lowercase 'main' instead of 'Main'
• Missing static keyword
• Incorrect parameter type or missing array brackets

3.

What will be the output of the following C# program?

using System;
class Program {
    static void Main(string[] args) {
        Console.WriteLine(args.Length);
    }
}

Assuming the program is run with command line arguments: apple banana cherry

medium

A. 0

B. 3

C. apple banana cherry

D. Compilation error

Solution

1. Step 1: Understand args parameter

   The args array contains command line arguments passed to the program.

2. Step 2: Count the arguments passed

   Three arguments are passed: "apple", "banana", and "cherry". So, args.Length is 3.

3. Final Answer:

   3 -> Option B

4. Quick Check:

   args.Length = 3 [OK]

Hint: args.Length counts command line arguments [OK]

Common Mistakes:

• Assuming args is empty without arguments
• Printing args directly instead of args.Length
• Confusing args with program output

4.

Identify the error in this C# program:

class Test {
    void Main() {
        System.Console.WriteLine("Hello World");
    }
}

medium

A. Main method must be static.

B. Missing namespace declaration.

C. Console.WriteLine syntax is incorrect.

D. Class must be public.

Solution

1. Step 1: Check Main method modifiers

   Main must be declared static because it is the entry point and called without an instance.

2. Step 2: Verify other elements

   Namespace and class access modifiers are optional; Console.WriteLine syntax is correct.

3. Final Answer:

   Main method must be static. -> Option A

4. Quick Check:

   Main must be static [OK]

Hint: Main must be static to run without object [OK]

Common Mistakes:

• Forgetting static keyword on Main
• Thinking namespace is mandatory
• Assuming class must be public

5.

You want your C# program to return an exit code to the operating system after running. Which Main method signature should you use?

hard

A. static void Main()

B. public static void Main(string[] args)

C. public static int Main(string[] args)

D. int Main() static

Solution

1. Step 1: Understand return type for exit code

   To return an exit code, Main must return an int representing the status.

2. Step 2: Check valid signatures

   public static int Main(string[] args) uses public static int Main(string[] args), which allows returning an integer exit code.

3. Final Answer:

   public static int Main(string[] args) -> Option C

4. Quick Check:

   Main returns int for exit code [OK]

Hint: Use int return type in Main to send exit code [OK]

Common Mistakes:

• Using void return type when exit code needed
• Incorrect method modifiers order
• Missing static keyword