Object type as universal base in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code using object as base?

Consider this C# code where object is used as a universal base type. What will be printed?

C Sharp (C#)

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

A System.Int32

B System.Object

C 123

D System.String

💡 Hint

Remember that object can hold any type, but GetType() returns the actual runtime type.

The variable val holds an integer value 123. Although declared as object, the actual type is System.Int32. So GetType() returns System.Int32.

❓ Predict Output

intermediate

What is the output when casting object to string?

What will this code print?

C Sharp (C#)

object val = "hello";
string s = (string)val;
Console.WriteLine(s.Length);

A System.String

B 5

C hello

D Runtime error

💡 Hint

Check the length of the string stored inside the object.

The object val holds a string "hello". Casting it back to string works fine. The length of "hello" is 5.

🔧 Debug

advanced

Why does this code cause an exception?

Examine the code below. Why does it throw an exception at runtime?

C Sharp (C#)

object val = 42;
string s = (string)val;
Console.WriteLine(s);

A Compile-time error due to invalid cast

B NullReferenceException because val is null

C InvalidCastException because int cannot be cast to string

D No exception, prints 42

💡 Hint

Think about what types can be cast directly to string.

The variable val holds an int boxed as object. Casting directly to string causes InvalidCastException because int and string are unrelated types.

🧠 Conceptual

advanced

What is the result of using object.Equals with different types?

What does this code print?

C Sharp (C#)

object a = 10;
object b = "10";
Console.WriteLine(a.Equals(b));

A False

B Runtime exception

C Compile-time error

D True

💡 Hint

Check if Equals compares values or types.

The Equals method returns false because a is an int and b is a string, so they are not equal.

❓ Predict Output

expert

What is the output of this polymorphic object array?

Given this array of objects holding different types, what will be printed?

C Sharp (C#)

object[] arr = { 1, "two", 3.0 };
foreach (var item in arr)
{
    Console.WriteLine(item.GetType().Name);
}

A

1
two
3.0

B

Object
Object
Object

C

int
string
double

D

Int32
String
Double

💡 Hint

Remember GetType() returns the runtime type of each element.

The array holds an int, a string, and a double boxed as objects. GetType().Name returns their actual type names: Int32, String, Double.

Practice

1. What is the role of the object type in C#?

easy

A. object is used only for reference types, not value types.

B. object is used only for strings.

C. object is a special type for numeric calculations.

D. object is the universal base type for all data types.

Solution

1. Step 1: Understand the base type concept

   In C#, object is the root type from which all other types derive, including value and reference types.

2. Step 2: Analyze the options

   Only object is the universal base type for all data types. correctly states that object is the universal base type for all data types.

3. Final Answer:

   object is the universal base type for all data types. -> Option D

4. Quick Check:

   object = universal base type [OK]

Hint: Remember: all types inherit from object in C# [OK]

Common Mistakes:

• Thinking object is only for reference types
• Confusing object with string or numeric types
• Assuming object is a special numeric type

2. Which of the following is the correct way to store an integer value in an object variable?

easy

A. int obj = new object(42);

B. object obj = 42;

C. object obj = new int(42);

D. object obj = "42";

Solution

1. Step 1: Understand boxing of value types

   In C#, value types like int can be stored in an object variable by implicit boxing, e.g., object obj = 42;.

2. Step 2: Check each option

   object obj = 42; correctly assigns an integer to an object variable. Options B and C use invalid syntax. object obj = "42"; stores a string, not an integer.

3. Final Answer:

   object obj = 42; -> Option B

4. Quick Check:

   Boxing int to object = object obj = 42; [OK]

Hint: Assign value directly to object for boxing [OK]

Common Mistakes:

• Trying to use new with int type
• Confusing string and int assignments
• Using invalid constructors for value types

3. What will be the output of this code?

object obj = 10;
int x = (int)obj + 5;
Console.WriteLine(x);

medium

A. Runtime error

B. 10

C. 15

D. Compilation error

Solution

1. Step 1: Understand boxing and unboxing

   The integer 10 is boxed into obj. Casting back to int unboxes it correctly.

2. Step 2: Calculate the expression

   Unboxed value 10 plus 5 equals 15, which is printed.

3. Final Answer:

   15 -> Option C

4. Quick Check:

   Unbox 10 + 5 = 15 [OK]

Hint: Cast object back to int before arithmetic [OK]

Common Mistakes:

• Forgetting to cast before adding
• Expecting string output
• Confusing compile and runtime errors

4. Identify the error in this code snippet:

object obj = "hello";
int num = (int)obj;
Console.WriteLine(num);

medium

A. Invalid cast exception at runtime

B. Compilation error due to type mismatch

C. No error, prints 'hello'

D. Syntax error in variable declaration

Solution

1. Step 1: Analyze the cast operation

   The object contains a string "hello" but is cast to int, which is invalid.

2. Step 2: Identify the error type

   This causes an InvalidCastException at runtime, not a compile-time error.

3. Final Answer:

   Invalid cast exception at runtime -> Option A

4. Quick Check:

   Wrong cast string to int = runtime error [OK]

Hint: Cast only to the original stored type [OK]

Common Mistakes:

• Assuming compile-time error instead of runtime
• Casting string to int directly
• Ignoring exception possibility

5. Given this code, what is the best way to safely retrieve the integer value stored in obj?

object obj = 25;
// Retrieve integer value safely here

hard

A. int value = obj is int i ? i : 0;

B. int value = obj as int;

C. int value = Convert.ToInt32(obj);

D. int value = (int)obj;

Solution

1. Step 1: Understand safe casting options

   Direct cast (A) can throw exceptions. as operator (B) cannot be used with value types like int.

2. Step 2: Evaluate options for safety

   int value = obj is int i ? i : 0; uses pattern matching to check type before assignment, avoiding exceptions. int value = Convert.ToInt32(obj); converts but may throw if obj is not convertible.

3. Final Answer:

   int value = obj is int i ? i : 0; -> Option A

4. Quick Check:

   Use pattern matching for safe unboxing [OK]

Hint: Use pattern matching to safely cast object [OK]

Common Mistakes:

• Using 'as' with value types
• Not checking type before casting
• Assuming Convert.ToInt32 is always safe