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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of static and instance members

What is the output of this C# code?

C Sharp (C#)

class Counter {
    public static int count = 0;
    public int instanceCount = 0;

    public Counter() {
        count++;
        instanceCount++;
    }
}

class Program {
    static void Main() {
        Counter a = new Counter();
        Counter b = new Counter();
        System.Console.WriteLine($"Static count: {Counter.count}");
        System.Console.WriteLine($"a.instanceCount: {a.instanceCount}");
        System.Console.WriteLine($"b.instanceCount: {b.instanceCount}");
    }
}

A

Static count: 2
a.instanceCount: 1
b.instanceCount: 1

B

Static count: 1
a.instanceCount: 2
b.instanceCount: 2

C

Static count: 2
a.instanceCount: 2
b.instanceCount: 2

D

Static count: 0
a.instanceCount: 1
b.instanceCount: 1

💡 Hint

Remember static members are shared across all instances, instance members belong to each object.

The static variable count is shared by all instances, so it increments twice.

The instance variable instanceCount is unique to each object, so each has value 1.

🧠 Conceptual

intermediate

Understanding static member access

Which statement about static members in C# is TRUE?

A Static members cannot be accessed from static methods.

B Static members can be accessed without creating an instance of the class.

C Static members are unique to each instance of the class.

D Static members can only be accessed through an instance of the class.

💡 Hint

Think about how you call static methods like Math.Sqrt without creating a Math object.

Static members belong to the class itself, so you can access them directly using the class name without creating an object.

❓ Predict Output

advanced

Static constructor behavior

What will be printed when this C# program runs?

C Sharp (C#)

class Example {
    public static int value;

    static Example() {
        value = 10;
        System.Console.WriteLine("Static constructor called");
    }

    public Example() {
        value += 5;
        System.Console.WriteLine("Instance constructor called");
    }
}

class Program {
    static void Main() {
        System.Console.WriteLine(Example.value);
        Example e = new Example();
        System.Console.WriteLine(Example.value);
    }
}

A

Static constructor called
0
Instance constructor called
15

B

0
Instance constructor called
15

C

Static constructor called
10
Instance constructor called
15

D

Static constructor called
10
Instance constructor called
10

💡 Hint

Static constructors run once before any instance or static member is accessed.

The static constructor runs first and sets value to 10 and prints a message.

Then Main prints 10.

Creating an instance calls the instance constructor, adds 5 to value, and prints a message.

Finally, value is 15.

🔧 Debug

advanced

Why does this code cause an error?

This code tries to access an instance member from a static method. What error will it cause?

C Sharp (C#)

class Sample {
    public int number = 5;

    public static void ShowNumber() {
        System.Console.WriteLine(number);
    }
}

A Compile-time error: An object reference is required for the non-static field 'number'.

B Runtime error: NullReferenceException

C No error, prints 5

D Compile-time error: Static method cannot be declared in a class

💡 Hint

Static methods cannot access instance variables directly because they don't belong to an object.

The static method ShowNumber tries to access the instance field number without an object.

This causes a compile-time error requiring an object reference.

🚀 Application

expert

Predict the final value of static and instance members

Given the following code, what is the final output?

C Sharp (C#)

class Tracker {
    public static int totalCount = 0;
    public int instanceCount = 0;

    public Tracker() {
        totalCount++;
        instanceCount++;
    }

    public void Increment() {
        totalCount++;
        instanceCount++;
    }
}

class Program {
    static void Main() {
        Tracker t1 = new Tracker();
        Tracker t2 = new Tracker();
        t1.Increment();
        t2.Increment();
        System.Console.WriteLine($"Total count: {Tracker.totalCount}");
        System.Console.WriteLine($"t1 instance count: {t1.instanceCount}");
        System.Console.WriteLine($"t2 instance count: {t2.instanceCount}");
    }
}

A

Total count: 6
t1 instance count: 2
t2 instance count: 2

B

Total count: 4
t1 instance count: 1
t2 instance count: 1

C

Total count: 6
t1 instance count: 1
t2 instance count: 1

D

Total count: 4
t1 instance count: 2
t2 instance count: 2

💡 Hint

Count how many times static and instance variables are incremented.

Each constructor call increments totalCount and instanceCount by 1.

Two objects created: totalCount = 2, each instanceCount = 1.

Each Increment call adds 1 to both counts.

Two increments called: totalCount +2, each instanceCount +1.

Final totalCount = 4 (2 from constructors + 2 from increments), each instanceCount = 1 + 1 = 2.