Getting type information at runtime in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Type Name Retrieval

What is the output of this C# code snippet?

C Sharp (C#)

int number = 42;
Console.WriteLine(number.GetType().Name);

A "System.Int32"

B "int"

C "Number"

D "Int32"

💡 Hint

Use GetType() and check the Name property.

The GetType() method returns the runtime type of the object. The Name property returns the simple name of the type, which for an int is "Int32".

❓ Predict Output

intermediate

Output of Checking Type Equality

What will this code print?

C Sharp (C#)

object obj = "hello";
if (obj.GetType() == typeof(string))
    Console.WriteLine("Match");
else
    Console.WriteLine("No Match");

A Match

B No Match

C Compilation error

D Runtime exception

💡 Hint

Compare the runtime type of obj with typeof(string).

The object obj holds a string, so obj.GetType() returns System.String, which equals typeof(string).

🔧 Debug

advanced

Identify the Error in Type Checking

What error does this code produce when run?

C Sharp (C#)

object val = null;
if (val.GetType() == typeof(object))
    Console.WriteLine("Object");
else
    Console.WriteLine("Not Object");

A Prints "Not Object"

B Prints "Object"

C NullReferenceException

D Compilation error

💡 Hint

Check what happens when calling GetType() on null.

Calling GetType() on a null reference causes a NullReferenceException at runtime.

🧠 Conceptual

advanced

Understanding typeof vs GetType()

Which statement is true about typeof and GetType() in C#?

A typeof gets the compile-time type; GetType() gets the runtime type of an instance

B typeof gets the runtime type; GetType() gets the compile-time type

C Both typeof and GetType() return the same type information always

D typeof can only be used on variables; GetType() only on types

💡 Hint

Think about when you use typeof and when you call GetType().

typeof is used with a type name at compile time, while GetType() is called on an instance to get its runtime type.

❓ Predict Output

expert

Output of Type Checking with Inheritance

What is the output of this code?

C Sharp (C#)

class Animal {}
class Dog : Animal {}

Animal pet = new Dog();
Console.WriteLine(pet.GetType() == typeof(Animal));

A True

B False

C Compilation error

D Runtime exception

💡 Hint

GetType() returns the actual runtime type, not the declared type.

pet is declared as Animal but holds a Dog instance. GetType() returns Dog, which is not equal to typeof(Animal).

Practice

1. What does the GetType() method do in C#?

easy

A. Changes the type of an object

B. Creates a new object of a specified type

C. Returns the exact runtime type of an object

D. Deletes the object from memory

Solution

1. Step 1: Understand the purpose of GetType()

   The GetType() method is used to find out the exact type of an object while the program is running.

2. Step 2: Differentiate from other actions

   It does not change, create, or delete objects; it only returns type information.

3. Final Answer:

   Returns the exact runtime type of an object -> Option C

4. Quick Check:

   GetType() returns type info [OK]

Hint: Remember: GetType() tells you what type an object is [OK]

Common Mistakes:

• Thinking GetType() changes the object
• Confusing GetType() with creating objects
• Assuming GetType() deletes objects

2. Which of the following is the correct syntax to get the type of an object obj in C#?

easy

A. obj.GetType()

B. GetType(obj)

C. typeof(obj)

D. obj.Type()

Solution

1. Step 1: Recall method call syntax

   In C#, to get the runtime type of an object, you call the method on the object: obj.GetType().

2. Step 2: Understand other options

   GetType(obj) is invalid syntax, typeof(obj) is incorrect because typeof expects a type name, not a variable, and obj.Type() does not exist.

3. Final Answer:

   obj.GetType() -> Option A

4. Quick Check:

   Call GetType() on the object [OK]

Hint: Use dot notation: object.GetType() [OK]

Common Mistakes:

• Using typeof with a variable instead of a type
• Trying to call GetType as a standalone function
• Using incorrect method names like Type()

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

object val = 123;
Console.WriteLine(val.GetType().Name);

medium

A. Int32

B. int

C. Object

D. String

Solution

1. Step 1: Identify the runtime type of val

   The variable val is declared as object but holds the integer value 123, which is of type Int32 in C#.

2. Step 2: Understand GetType().Name output

   Calling val.GetType().Name returns the name of the actual runtime type, which is Int32.

3. Final Answer:

   Int32 -> Option A

4. Quick Check:

   Runtime type name = Int32 [OK]

Hint: GetType().Name shows exact type name [OK]

Common Mistakes:

• Expecting 'int' instead of 'Int32'
• Thinking it returns 'Object' because of variable type
• Confusing with string output

4. Identify the error in this code snippet:

object data = "hello";
if (data.GetType() == string)
{
    Console.WriteLine("It's a string!");
}

medium

A. Missing semicolon after Console.WriteLine

B. Comparing GetType() to a type name instead of a Type object

C. Using == instead of .Equals() for type comparison

D. GetType() cannot be used on object variables

Solution

1. Step 1: Analyze the type comparison

   The code compares data.GetType() to string, but string is a keyword, not a Type object.

2. Step 2: Correct way to compare types

   To compare types, use typeof(string) which returns the Type object for string. So the condition should be data.GetType() == typeof(string).

3. Final Answer:

   Comparing GetType() to a type name instead of a Type object -> Option B

4. Quick Check:

   Use typeof(TypeName) for type comparison [OK]

Hint: Compare with typeof(TypeName), not just type name [OK]

Common Mistakes:

• Using type name without typeof()
• Thinking == can't compare types
• Assuming GetType() is invalid on object

5. You want to write a method that accepts an object and prints a special message if the object is an integer or a string. Which code correctly uses runtime type information to do this?

void CheckType(object obj)
{
    if (obj.GetType() == typeof(int))
        Console.WriteLine("Integer detected");
    else if (obj.GetType() == typeof(string))
        Console.WriteLine("String detected");
    else
        Console.WriteLine("Other type");
}

hard

A. The code should compare obj.GetType().Name to string literals

B. This code should use obj is int instead of GetType()

C. GetType() cannot be used inside methods

D. This code correctly checks types using GetType() and typeof()

Solution

1. Step 1: Understand the method logic

   The method uses obj.GetType() to get the runtime type and compares it with typeof(int) and typeof(string) to identify the type.

2. Step 2: Verify correctness of type checks

   This is a valid and common way to check exact types at runtime in C#. Using GetType() with typeof() is correct and safe.

3. Final Answer:

   This code correctly checks types using GetType() and typeof() -> Option D

4. Quick Check:

   GetType() + typeof() = correct type check [OK]

Hint: Use GetType() == typeof(Type) for exact type checks [OK]

Common Mistakes:

• Thinking GetType() can't be used in methods
• Using 'is' when exact type match is needed
• Comparing type names as strings instead of Type objects