Stack vs heap mental model in C Sharp (C#) - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# code involving stack and heap?

Consider the following C# code snippet. What will be printed to the console?

C Sharp (C#)

using System;
class Program {
    static void Main() {
        int x = 10;
        int y = x;
        y = 20;
        Console.WriteLine(x);
    }
}

A 0

B 20

C 10

D Compilation error

💡 Hint

Think about where value types like int are stored and how assignment works.

Variables x and y are value types stored on the stack. Assigning y = x copies the value. Changing y does not affect x. So x remains 10.

❓ Predict Output

intermediate

What is the output when modifying a reference type?

Look at this C# code. What will it print?

C Sharp (C#)

using System;
class Program {
    class Box { public int Value; }
    static void Main() {
        Box a = new Box();
        a.Value = 5;
        Box b = a;
        b.Value = 10;
        Console.WriteLine(a.Value);
    }
}

A 10

B Compilation error

C 0

D 5

💡 Hint

Remember that classes are reference types stored on the heap.

Both a and b point to the same object on the heap. Changing b.Value changes the object, so a.Value is also 10.

🧠 Conceptual

advanced

Which statement best describes stack and heap in C#?

Choose the statement that correctly explains the difference between stack and heap memory in C#.

A Stack and heap are the same memory area but used differently.

B Stack stores value types and method call info; heap stores reference type objects.

C Heap stores local variables and method parameters; stack stores objects created with <code>new</code>.

D Stack stores reference types and heap stores value types.

💡 Hint

Think about where value types and reference types are stored during execution.

In C#, the stack holds value types and method call info (like parameters and local variables). The heap stores objects created by reference types.

🔧 Debug

advanced

Why does this code cause a NullReferenceException?

Examine the code below. Why does it throw a NullReferenceException?

C Sharp (C#)

using System;
class Program {
    class Container { public string Text; }
    static void Main() {
        Container c = null;
        c.Text = "Hello";
        Console.WriteLine(c.Text);
    }
}

A Because <code>c</code> is null and accessing <code>Text</code> causes an error.

B Because <code>Text</code> is not initialized to a string.

C Because <code>Console.WriteLine</code> cannot print strings.

D Because <code>Container</code> is a value type and cannot be null.

💡 Hint

Think about what happens when you try to access a member of a null reference.

c is a reference type variable set to null. Trying to access c.Text causes a NullReferenceException because there is no actual object.

🚀 Application

expert

How many objects are created on the heap after this code runs?

Consider this C# code snippet. How many objects are created on the heap after Main finishes?

C Sharp (C#)

using System;
class Program {
    class Node {
        public int Value;
        public Node Next;
    }
    static void Main() {
        Node first = new Node();
        first.Value = 1;
        Node second = new Node();
        second.Value = 2;
        first.Next = second;
        Node third = second;
    }
}

A 0

B 1

C 3

D 2

💡 Hint

Count how many times new is used to create objects.

Two new Node() calls create two objects on the heap. The variable third just references the existing second object.