Why generics are needed in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of non-generic collection usage

What is the output of this C# code that uses a non-generic ArrayList to store integers and strings?

C Sharp (C#)

using System;
using System.Collections;

class Program {
    static void Main() {
        ArrayList list = new ArrayList();
        list.Add(10);
        list.Add("hello");
        int sum = 0;
        foreach (var item in list) {
            if (item is int) {
                sum += (int)item;
            }
        }
        Console.WriteLine(sum);
    }
}

A 0

B hello

C 10

D Runtime error

💡 Hint

Look at how the code sums only integers in the list.

The ArrayList contains 10 and "hello". The loop adds only integers to sum, so sum is 10.

❓ Predict Output

intermediate

Output of generic List usage

What is the output of this C# code that uses a generic List to store integers?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> list = new List<int>();
        list.Add(10);
        list.Add(20);
        int sum = 0;
        foreach (int item in list) {
            sum += item;
        }
        Console.WriteLine(sum);
    }
}

A 30

B 10 20

C 20

D Compilation error

💡 Hint

Sum all integers in the list.

The list contains 10 and 20. The sum is 30.

🔧 Debug

advanced

Why does this code cause a runtime error?

This code uses a non-generic ArrayList but throws an exception at runtime. Why?

C Sharp (C#)

using System;
using System.Collections;

class Program {
    static void Main() {
        ArrayList list = new ArrayList();
        list.Add(10);
        list.Add("hello");
        int total = 0;
        foreach (int item in list) {
            total += item;
        }
        Console.WriteLine(total);
    }
}

A IndexOutOfRangeException because of foreach

B InvalidCastException because "hello" cannot be cast to int

C No error, output is 10

D NullReferenceException because list is null

💡 Hint

Check the type casting inside the foreach loop.

The foreach tries to cast "hello" to int, causing InvalidCastException.

🧠 Conceptual

advanced

Why use generics instead of non-generic collections?

Which of the following is the main reason to use generics in C# collections?

A To avoid runtime errors by enforcing type safety at compile time

B To make code run slower but use less memory

C To allow storing any type without restrictions

D To make code compatible only with older .NET versions

💡 Hint

Think about when errors happen with non-generic collections.

Generics enforce type safety at compile time, preventing runtime casting errors.

❓ Predict Output

expert

Output of generic method with type parameter

What is the output of this C# code using a generic method to print the type and value?

C Sharp (C#)

using System;

class Program {
    static void PrintValue<T>(T value) {
        Console.WriteLine($"Type: {typeof(T)}, Value: {value}");
    }

    static void Main() {
        PrintValue(123);
        PrintValue("abc");
        PrintValue(3.14);
    }
}

A

Type: T, Value: 123
Type: T, Value: abc
Type: T, Value: 3.14

B Compilation error due to generic method

C

Type: System.Object, Value: 123
Type: System.Object, Value: abc
Type: System.Object, Value: 3.14

D

Type: System.Int32, Value: 123
Type: System.String, Value: abc
Type: System.Double, Value: 3.14

💡 Hint

typeof(T) shows the actual type used when calling the method.

The generic method prints the actual type of each argument and its value.