Struct declaration and behavior in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of struct value assignment

What is the output of this C# code?

C Sharp (C#)

struct Point {
    public int X;
    public int Y;
}

class Program {
    static void Main() {
        Point p1 = new Point { X = 5, Y = 10 };
        Point p2 = p1;
        p2.X = 20;
        System.Console.WriteLine(p1.X);
    }
}

A 20

B 5

C 0

D Compilation error

💡 Hint

Remember that structs are value types and copying creates a new copy.

Structs are value types in C#. Assigning p1 to p2 copies the values. Changing p2.X does not affect p1.X. So p1.X remains 5.

❓ Predict Output

intermediate

Struct method modifying fields

What is the output of this C# program?

C Sharp (C#)

struct Counter {
    public int Count;
    public void Increment() {
        Count++;
    }
}

class Program {
    static void Main() {
        Counter c = new Counter();
        c.Increment();
        System.Console.WriteLine(c.Count);
    }
}

A 1

B Runtime error

C Compilation error

D 0

💡 Hint

Instance methods on structs operate on a copy of the struct.

When calling c.Increment(), the method operates on the instance c directly, incrementing Count to 1. So c.Count is 1.

❓ Predict Output

advanced

Struct boxing and method call effect

What is the output of this C# code?

C Sharp (C#)

struct Number {
    public int Value;
    public void DoubleValue() {
        Value *= 2;
    }
}

class Program {
    static void Main() {
        Number n = new Number { Value = 10 };
        object o = n;
        ((Number)o).DoubleValue();
        System.Console.WriteLine(n.Value);
    }
}

A Compilation error

B 20

C 10

D Runtime error

💡 Hint

Think about what happens when a struct is boxed.

Boxing creates a copy of the struct on the heap. Calling DoubleValue on the boxed copy involves unboxing to a stack copy, modifying that, but does not change the original n or the boxed copy. So n.Value remains 10.

❓ Predict Output

advanced

Struct default constructor behavior

What is the output of this C# program?

C Sharp (C#)

struct Data {
    public int Number;
    public string Text;
}

class Program {
    static void Main() {
        Data d = new Data();
        System.Console.WriteLine($"{d.Number}, {d.Text ?? "null"}");
    }
}

A 0, null

B 0, ""

C Compilation error

D Runtime error

💡 Hint

Struct fields get default values when using the default constructor.

Struct fields are automatically initialized to their default values. Number is 0 and Text is null.

🧠 Conceptual

expert

Struct immutability and method behavior

Consider this struct and code snippet. Which statement is true about the output?

struct ImmutablePoint {
    public int X { get; init; }
    public int Y { get; init; }
    public ImmutablePoint(int x, int y) {
        X = x;
        Y = y;
    }
    public ImmutablePoint Move(int dx, int dy) {
        return new ImmutablePoint(X + dx, Y + dy);
    }
}

class Program {
    static void Main() {
        ImmutablePoint p = new ImmutablePoint(1, 2);
        p.Move(3, 4);
        System.Console.WriteLine($"{p.X}, {p.Y}");
    }
}

A Runtime error due to uninitialized properties.

B The output is '4, 6' because Move modifies the struct fields directly.

C Compilation error because properties have no setters.

D The output is '1, 2' because structs are immutable and Move returns a new struct without changing p.

💡 Hint

Think about how immutable structs behave and what the Move method returns.

The Move method returns a new ImmutablePoint with updated coordinates but does not change the original p. Since p is not reassigned, its values remain (1, 2).