Static members vs instance members in C Sharp (C#) - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a static integer variable named count.

C Sharp (C#)

public class Counter {
    public static int [1];
}

Drag options to blanks, or click blank then click option'

Atotal

Bvalue

Ccount

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance variable syntax instead of static.

Choosing a variable name other than 'count'.

The static variable is named count as required.

2fill in blank

medium

Complete the code to access the static member count from the class Counter.

C Sharp (C#)

int currentCount = Counter.[1];

Drag options to blanks, or click blank then click option'

Avalue

Bnumber

Ctotal

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access static member via an instance.

Using a wrong member name.

Static members are accessed using the class name. Here, count is the static member.

3fill in blank

hard

Complete the code to access the instance member value without an object.

C Sharp (C#)

public class Item {
    public int value;
}

int x = Item.[1];

Drag options to blanks, or click blank then click option'

Avalue

Bcount

Cnumber

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access instance members without creating an object.

Confusing static and instance members.

Instance members cannot be accessed directly from the class. This code causes an error because value is an instance member.

4fill in blank

hard

Fill both blanks to create an instance of Item and access its value member.

C Sharp (C#)

Item item = new [1]();
int val = item.[2];

Drag options to blanks, or click blank then click option'

AItem

BCounter

Cvalue

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong class name to create the object.

Trying to access static members as instance members.

You create an instance of Item and access its instance member value.

5fill in blank

hard

Fill all three blanks to declare a static method that returns the static count variable.

C Sharp (C#)

public class Counter {
    public static int count;
    public static int [1]() {
        return [2].[3];
    }
}

Drag options to blanks, or click blank then click option'

AGetCount

BCounter

Ccount

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access static variables without the class name inside static methods.

Using instance member names instead of static ones.

The static method GetCount returns the static variable count accessed via the class name Counter.

Practice

1. Which statement correctly describes a static member in C#?

easy

A. It belongs to the class and is shared by all instances.

B. It belongs to each object and stores unique data.

C. It can only be accessed through an object instance.

D. It is created every time a new object is instantiated.

Solution

1. Step 1: Understand static member concept

   Static members belong to the class itself, not to any individual object.

2. Step 2: Compare with instance members

   Instance members belong to objects and hold unique data per object, unlike static members.

3. Final Answer:

   It belongs to the class and is shared by all instances. -> Option A

4. Quick Check:

   Static member = shared by class [OK]

Hint: Static = shared by class, instance = unique per object [OK]

Common Mistakes:

• Confusing static with instance members
• Thinking static members are unique per object
• Believing static members require object to access

2. Which of the following is the correct way to declare a static field in a C# class?

easy

A. public static int count;

B. public int static count;

C. public int count;

D. int static public count;

Solution

1. Step 1: Recall C# static field syntax

   The correct order is access modifier, then 'static', then type and name.

2. Step 2: Check each option

   public static int count; matches the correct syntax: 'public static int count;'. Others have wrong order or missing keywords.

3. Final Answer:

   public static int count; -> Option A

4. Quick Check:

   Access modifier + static + type + name [OK]

Hint: Use 'public static' before type for static fields [OK]

Common Mistakes:

• Placing 'static' after the type
• Omitting 'static' keyword
• Incorrect order of keywords

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

class Counter {
    public static int count = 0;
    public Counter() {
        count++;
    }
}

class Program {
    static void Main() {
        Counter c1 = new Counter();
        Counter c2 = new Counter();
        Console.WriteLine(Counter.count);
    }
}

medium

A. 0

B. 2

C. 1

D. Compilation error

Solution

1. Step 1: Understand static field behavior

   The static field 'count' is shared by all instances and starts at 0.

2. Step 2: Trace constructor calls

   Each new Counter() increments 'count' by 1. Two objects created, so count becomes 2.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   Static count increments twice = 2 [OK]

Hint: Static fields keep shared state across all objects [OK]

Common Mistakes:

• Thinking count resets per object
• Confusing instance and static fields
• Expecting compilation error due to static access

4. Identify the error in this C# code snippet:

class Example {
    public static int value = 10;
    public int GetValue() {
        return value;
    }
}

medium

A. Cannot access static field 'value' inside instance method.

B. Method GetValue must be static to access static field 'value'.

C. Static field 'value' must be private.

D. No error; code compiles and runs correctly.

Solution

1. Step 1: Check static field access rules

   Instance methods can access static fields directly without error.

2. Step 2: Verify code correctness

   Method GetValue returns static field 'value' correctly; no syntax or access errors.

3. Final Answer:

   No error; code compiles and runs correctly. -> Option D

4. Quick Check:

   Instance method can access static field [OK]

Hint: Instance methods can access static fields directly [OK]

Common Mistakes:

• Thinking instance methods cannot access static fields
• Believing GetValue must be static
• Assuming static fields must be private

5. You want to count how many objects of a class are created, but also keep a unique ID for each object starting from 1. Which approach correctly uses static and instance members?

hard

A. Use only instance fields for both counter and ID.

B. Use an instance counter incremented in constructor; assign its value to a static ID field.

C. Use a static counter incremented in constructor; assign its value to an instance ID field.

D. Use static fields for both counter and ID without instance fields.

Solution

1. Step 1: Understand counting objects with static field

   A static counter shared by all objects can track total created objects.

2. Step 2: Assign unique ID per object using instance field

   Each object gets its own instance ID assigned from the static counter value.

3. Final Answer:

   Use a static counter incremented in constructor; assign its value to an instance ID field. -> Option C

4. Quick Check:

   Static counter + instance ID = unique IDs [OK]

Hint: Static counts total; instance stores unique ID per object [OK]

Common Mistakes:

• Using instance counter for total count
• Assigning static ID per object (not unique)
• Not incrementing counter in constructor