Method declaration and calling in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a method call with parameters

What is the output of the following C# program?

C Sharp (C#)

using System;
class Program {
    static int Multiply(int a, int b) {
        return a * b;
    }
    static void Main() {
        Console.WriteLine(Multiply(3, 4));
    }
}

A Error: Method Multiply not found

B 7

C 12

D 34

💡 Hint

Look at what the Multiply method returns when given 3 and 4.

The Multiply method returns the product of a and b. 3 * 4 = 12, so the output is 12.

❓ Predict Output

intermediate

Return value from a void method

What will happen when this C# code runs?

C Sharp (C#)

using System;
class Program {
    static void PrintMessage() {
        Console.WriteLine("Hello World");
    }
    static void Main() {
        var result = PrintMessage();
        Console.WriteLine(result == null);
    }
}

A Hello World\nTrue

B Compilation error: Cannot assign void to variable

C Hello World\nFalse

D Runtime error

💡 Hint

Void methods do not return a value and cannot be assigned to a variable.

In C#, you cannot assign the result of a void method to a variable because void methods do not return a value. This causes a compilation error.

❓ Predict Output

advanced

Method overloading and output

What is the output of this C# program?

C Sharp (C#)

using System;
class Program {
    static void Display(int x) {
        Console.WriteLine("Int: " + x);
    }
    static void Display(string x) {
        Console.WriteLine("String: " + x);
    }
    static void Main() {
        Display(5);
        Display("5");
    }
}

A String: 5\nInt: 5

B Runtime error

C Compilation error: Ambiguous call to Display

D Int: 5\nString: 5

💡 Hint

Look at how method overloading works with different parameter types.

The method Display is overloaded for int and string. Calling Display(5) calls the int version, Display("5") calls the string version.

❓ Predict Output

advanced

Output of recursive method call

What will this C# program print?

C Sharp (C#)

using System;
class Program {
    static int Factorial(int n) {
        if (n <= 1) return 1;
        return n * Factorial(n - 1);
    }
    static void Main() {
        Console.WriteLine(Factorial(4));
    }
}

A 24

B 10

C Error: Stack overflow

D 1

💡 Hint

Factorial of 4 is 4 * 3 * 2 * 1.

The Factorial method calls itself recursively until n is 1 or less, multiplying all numbers down to 1. 4! = 24.

❓ Predict Output

expert

Effect of method parameters on output

Consider this C# code. What is the output after running Main?

C Sharp (C#)

using System;
class Program {
    static void ChangeValue(int x) {
        x = 10;
    }
    static void Main() {
        int a = 5;
        ChangeValue(a);
        Console.WriteLine(a);
    }
}

A 5

B 10

C Compilation error

D Runtime error

💡 Hint

Think about whether the method changes the original variable or just a copy.

In C#, method parameters are passed by value by default. ChangeValue changes only the copy of a, so a remains 5.

Practice

1. What is the correct way to declare a method named Greet that returns nothing and takes no parameters in C#?

easy

A. public Greet() void { }

B. void Greet[] { }

C. void Greet { }

D. public void Greet() { }

Solution

1. Step 1: Understand method declaration syntax

   A method declaration starts with an access modifier (like public), then the return type (void means no return), then the method name, and parentheses for parameters.

2. Step 2: Check each option's syntax

   public void Greet() { } correctly uses 'public void Greet() { }'. Options A, B, and D have syntax errors like wrong brackets or missing parentheses.

3. Final Answer:

   public void Greet() { } -> Option D

4. Quick Check:

   Method declaration = public void Greet() { } [OK]

Hint: Method syntax: access + return type + name + parentheses [OK]

Common Mistakes:

• Using square brackets [] instead of parentheses ()
• Omitting parentheses after method name
• Placing return type after method name

2. Which of the following is the correct way to call a method named CalculateSum that takes two integers as parameters?

easy

A. CalculateSum 5, 10;

B. CalculateSum[5, 10];

C. CalculateSum(5, 10);

D. CalculateSum{5, 10};

Solution

1. Step 1: Recall method call syntax

   To call a method, use its name followed by parentheses containing arguments separated by commas.

2. Step 2: Evaluate each option

   CalculateSum(5, 10); uses parentheses correctly. Options B, C, and D use incorrect brackets or omit parentheses, causing syntax errors.

3. Final Answer:

   CalculateSum(5, 10); -> Option C

4. Quick Check:

   Method call = name + parentheses + arguments [OK]

Hint: Call methods with parentheses and comma-separated arguments [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting parentheses when calling methods
• Using curly braces for method calls

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

public class Program {
  public static int Double(int x) {
    return x * 2;
  }
  public static void Main() {
    int result = Double(4);
    Console.WriteLine(result);
  }
}

medium

A. 8

B. 4

C. 16

D. Compilation error

Solution

1. Step 1: Understand the method Double

   The method takes an integer x and returns x multiplied by 2.

2. Step 2: Trace the method call in Main

   Double(4) returns 4 * 2 = 8, which is stored in result and printed.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   Double(4) = 8 [OK]

Hint: Multiply input by 2, then print result [OK]

Common Mistakes:

• Confusing return value with input
• Expecting 16 by squaring instead of doubling
• Thinking method does not return a value

4. Identify the error in the following method declaration and fix it:

public int AddNumbers(int a, int b) {
  int sum = a + b;
}

medium

A. Add a return statement: return sum;

B. Change method return type to void

C. Remove parameters from method

D. Add semicolon after method name

Solution

1. Step 1: Check method return type and body

   The method declares it returns an int but does not return any value.

2. Step 2: Fix by adding a return statement

   Adding return sum; returns the calculated value, matching the return type.

3. Final Answer:

   Add a return statement: return sum; -> Option A

4. Quick Check:

   Return value needed for non-void methods [OK]

Hint: Non-void methods must return a value [OK]

Common Mistakes:

• Forgetting to return a value in non-void methods
• Changing return type incorrectly
• Removing parameters unnecessarily

5. You want to create a method IsEven that returns true if a number is even, otherwise false. Which of the following is the correct method declaration and call to check if 7 is even?

hard

A. public bool IsEven(int num) { if(num / 2 == 0) return true; else return false; } ... bool result = IsEven(7);

B. public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7);

C. public void IsEven(int num) { if(num % 2 == 0) return true; else return false; } ... bool result = IsEven(7);

D. public int IsEven(int num) { return num % 2; } ... int result = IsEven(7);

Solution

1. Step 1: Check method return type and logic

   Method should return bool and use modulo (%) to check evenness. public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); correctly returns true if remainder is 0.

2. Step 2: Verify method call and variable type

   public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); calls IsEven(7) and stores result in a bool variable, matching the method return type.

3. Final Answer:

   public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); -> Option B

4. Quick Check:

   Use modulo and bool return for even check [OK]

Hint: Use 'return num % 2 == 0;' for even check [OK]

Common Mistakes:

• Using division instead of modulo for even check
• Returning int instead of bool
• Declaring method void but trying to return a value