Multiple generic parameters in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of generic class with two type parameters

What is the output of the following C# program?

C Sharp (C#)

using System;

class Pair<T, U>
{
    public T First { get; set; }
    public U Second { get; set; }

    public Pair(T first, U second)
    {
        First = first;
        Second = second;
    }

    public void Print()
    {
        Console.WriteLine($"{First} and {Second}");
    }
}

class Program
{
    static void Main()
    {
        var pair = new Pair<int, string>(5, "hello");
        pair.Print();
    }
}

A 5 and hello

B hello and 5

C 5hello

D Compilation error

💡 Hint

Look at how the generic parameters are used and printed in the Print method.

The Pair class has two generic parameters T and U. The Print method prints First and Second separated by ' and '. Since First is 5 and Second is "hello", the output is "5 and hello".

❓ Predict Output

intermediate

Output of generic method with two parameters

What is the output of this C# program?

C Sharp (C#)

using System;

class Utils
{
    public static void Swap<T, U>(ref T a, ref U b)
    {
        Console.WriteLine($"Swapping {a} and {b}");
    }
}

class Program
{
    static void Main()
    {
        int x = 10;
        string y = "test";
        Utils.Swap(ref x, ref y);
    }
}

A Swapping 10 and test

B Swapping test and 10

C Compilation error due to different types

D Runtime error

💡 Hint

Generic methods can have multiple type parameters and can accept different types.

The Swap method prints the values of a and b. Since a is 10 and b is "test", it prints "Swapping 10 and test".

🔧 Debug

advanced

Identify the error in generic class instantiation

What error does the following code produce?

C Sharp (C#)

class Container<T, U>
{
    public T Item1;
    public U Item2;
}

class Program
{
    static void Main()
    {
        Container<int> c = new Container<int, string>();
    }
}

A CS0029: Cannot implicitly convert type 'Container<int, string>' to 'Container<int>'

B CS0311: The type arguments for method cannot be inferred

C No error, compiles successfully

D CS0305: Using the generic type 'Container<T, U>' requires 2 type arguments

💡 Hint

Check how many generic parameters the class Container expects.

The class Container requires two type parameters but only one is provided in the declaration, causing CS0305 error.

📝 Syntax

advanced

Which option correctly declares a generic class with two parameters?

Select the correct syntax to declare a generic class with two type parameters T and U.

A class MyClass<T U> { }

B class MyClass<T; U> { }

C class MyClass<T, U> { }

D class MyClass<T> U { }

💡 Hint

Generic parameters are separated by commas inside angle brackets.

The correct syntax uses commas to separate generic parameters inside angle brackets: .

🚀 Application

expert

Determine the number of items in a generic dictionary

Given the following code, how many items are in the dictionary after execution?

C Sharp (C#)

using System.Collections.Generic;

class Program
{
    static void Main()
    {
        Dictionary<int, string> dict = new Dictionary<int, string>();
        dict.Add(1, "one");
        dict.Add(2, "two");
        dict[3] = "three";
        dict[2] = "deux";
    }
}

A 4

B 3

C 2

D Compilation error

💡 Hint

Adding a key that already exists updates its value, not adds a new item.

The dictionary has keys 1, 2, and 3. The value for key 2 is updated, so total items remain 3.

Practice

1.

What is the correct way to declare a generic class with two type parameters in C#?

class MyClass<T1, T2> { }

easy

A. class MyClass<T1> { }

B. class MyClass<T1, T2> { }

C. class MyClass<T1; T2> { }

D. class MyClass<T1 T2> { }

Solution

1. Step 1: Understand generic class syntax

   In C#, multiple generic parameters are separated by commas inside angle brackets <>.

2. Step 2: Check each option's syntax

   class MyClass<T1, T2> { } correctly uses a comma between T1 and T2. Other options use a single parameter, semicolon, or space which are incorrect.

3. Final Answer:

   class MyClass<T1, T2> { } -> Option B

4. Quick Check:

   Multiple generic parameters use commas inside <> [OK]

Hint: Separate generic types with commas inside angle brackets [OK]

Common Mistakes:

• Using semicolons or spaces instead of commas
• Forgetting to separate multiple generic parameters
• Declaring only one generic parameter when two are needed

2.

Which of the following is the correct syntax to declare a method with two generic parameters in C#?

public void Swap<T1, T2>(T1 a, T2 b) { }

easy

A. public void Swap<T1 T2>(T1 a, T2 b) { }

B. public void Swap<T1; T2>(T1 a, T2 b) { }

C. public void Swap<T1, T2>(T1 a, T2 b) { }

D. public void Swap(T1 a, T2 b) { }

Solution

1. Step 1: Recall method generic parameter syntax

   Generic parameters for methods are declared inside angle brackets <> separated by commas.

2. Step 2: Evaluate each option

   public void Swap<T1, T2>(T1 a, T2 b) { } correctly uses commas between T1 and T2. Other options use invalid separators like space or semicolon, or miss the generic parameters entirely.

3. Final Answer:

   public void Swap<T1, T2>(T1 a, T2 b) { } -> Option C

4. Quick Check:

   Method generics need commas inside <> [OK]

Hint: Use commas to separate generic parameters in method declarations [OK]

Common Mistakes:

• Omitting generic parameters in method signature
• Using spaces or semicolons instead of commas
• Placing generic parameters outside angle brackets

3.

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

class Pair<T1, T2> {
    public T1 First;
    public T2 Second;
    public Pair(T1 first, T2 second) {
        First = first;
        Second = second;
    }
    public override string ToString() {
        return $"{First} and {Second}";
    }
}

var p = new Pair<int, string>(5, "hello");
Console.WriteLine(p);

medium

A. 5, hello

B. Pair`2

C. System.Pair

D. 5 and hello

Solution

1. Step 1: Understand the Pair class and ToString override

   The Pair class stores two values and overrides ToString to return "{First} and {Second}".

2. Step 2: Analyze the instantiation and output

   We create Pair<int, string> with 5 and "hello". Console.WriteLine calls ToString, so output is "5 and hello".

3. Final Answer:

   5 and hello -> Option D

4. Quick Check:

   ToString returns "{First} and {Second}" [OK]

Hint: Check ToString override for output format [OK]

Common Mistakes:

• Assuming default ToString output for generic class
• Confusing comma with 'and' in output
• Ignoring ToString override

4.

Identify the error in the following code snippet:

class Container<T1, T2> {
    public T1 Item1;
    public T2 Item2;
    public Container(T1 item1, T2 item2) {
        Item1 = item1;
        Item2 = item2;
    }
}

var c = new Container<int>(5, 10);

medium

A. Missing second generic type argument when creating Container instance

B. Constructor parameters types do not match generic types

C. Cannot use int as generic type

D. Missing semicolon after class declaration

Solution

1. Step 1: Check generic parameters in class and instance

   The class Container requires two generic types: T1 and T2.

2. Step 2: Analyze the instance creation

   The code uses Container<int> with only one generic argument, but two are required.

3. Final Answer:

   Missing second generic type argument when creating Container instance -> Option A

4. Quick Check:

   Two generic parameters require two type arguments [OK]

Hint: Match number of generic arguments with parameters [OK]

Common Mistakes:

• Providing fewer generic arguments than declared
• Assuming default generic types
• Ignoring compiler errors about generic arguments

5.

Given the following generic method, what is the correct way to call it with two different types?

public static void PrintPair<T1, T2>(T1 first, T2 second) {
    Console.WriteLine($"First: {first}, Second: {second}");
}

Choose the correct call:

hard

A. PrintPair<int, string>(10, "test");

B. PrintPair<int>(10, "test");

C. PrintPair<T1, T2>(10, "test");

D. PrintPair<string, int>(10, "test");

Solution

1. Step 1: Understand generic method call syntax

   When calling a generic method with multiple parameters, specify all types inside <> in order.

2. Step 2: Match types with arguments

   The method expects T1 then T2. PrintPair<int, string>(10, "test"); uses <int, string> matching arguments 10 (int) and "test" (string). PrintPair<string, int>(10, "test"); reverses types incorrectly.

3. Final Answer:

   PrintPair<int, string>(10, "test"); -> Option A

4. Quick Check:

   Generic method call types match argument order [OK]

Hint: Specify all generic types in order when calling method [OK]

Common Mistakes:

• Providing fewer generic types than parameters
• Reversing generic types order
• Omitting generic types when required