Attribute declaration syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this attribute usage?

Consider the following C# code with a custom attribute applied to a class. What will be printed when the program runs?

C Sharp (C#)

using System;

[AttributeUsage(AttributeTargets.Class)]
public class InfoAttribute : Attribute
{
    public string Description { get; }
    public InfoAttribute(string description) => Description = description;
}

[Info("Sample class")] 
public class Sample {}

class Program
{
    static void Main()
    {
        var attr = (InfoAttribute)Attribute.GetCustomAttribute(typeof(Sample), typeof(InfoAttribute));
        Console.WriteLine(attr.Description);
    }
}

A Sample class

B InfoAttribute

C System.Attribute

D null

💡 Hint

Look at the Description property set by the attribute constructor.

The InfoAttribute is applied to the Sample class with the description "Sample class". Retrieving the attribute and printing its Description property outputs "Sample class".

❓ Predict Output

intermediate

What error occurs with this attribute declaration?

What error will this C# code produce when compiled?

C Sharp (C#)

[AttributeUsage(AttributeTargets.Method)]
public class MyAttribute : Attribute
{
    public int Value { get; set; }
}

[My(Value = 5)]
public class TestClass
{
    public void TestMethod() {}
}

A CS0246: The type or namespace name 'My' could not be found

B CS0106: The modifier 'public' is not valid for this item

C CS0592: Attribute 'My' is not valid on this declaration type. It is only valid on 'method' declarations.

D No error, compiles successfully

💡 Hint

Check where the attribute is allowed to be applied versus where it is used.

The attribute My is declared to be valid only on methods, but it is applied to a class. This causes a compilation error CS0592.

🔧 Debug

advanced

Why does this attribute constructor cause a compilation error?

Identify the reason for the compilation error in this attribute declaration code.

C Sharp (C#)

public class RangeAttribute : Attribute
{
    public int Min { get; }
    public int Max { get; }

    public RangeAttribute(int min, int max)
    {
        Min = min;
        Max = max;
    }

    public RangeAttribute(int min)
    {
        Min = min;
        Max = 100;
    }
}

A Error: Duplicate constructor definitions with the same signature

B No error, code compiles successfully

C Error: Attribute constructors must have only one parameter

D Error: Properties Min and Max must have setters

💡 Hint

Check if multiple constructors with different parameters are allowed in attributes.

Attributes can have multiple constructors with different parameters. Properties can be read-only if set in constructor. This code compiles fine.

❓ Predict Output

advanced

What is the output of this attribute with named parameters?

What will this program print when run?

C Sharp (C#)

using System;

[AttributeUsage(AttributeTargets.Class)]
public class InfoAttribute : Attribute
{
    public string Name { get; set; }
    public int Version { get; set; }
}

[Info(Name = "Test", Version = 2)]
public class Demo {}

class Program
{
    static void Main()
    {
        var attr = (InfoAttribute)Attribute.GetCustomAttribute(typeof(Demo), typeof(InfoAttribute));
        Console.WriteLine($"Name: {attr.Name}, Version: {attr.Version}");
    }
}

A Name: Test, Version: 2

B Name: , Version: 0

C Name: Test, Version: 0

D Name: , Version: 2

💡 Hint

Named parameters set properties after constructor runs.

The attribute sets Name and Version via named parameters. These values are printed exactly.

📝 Syntax

expert

Which attribute declaration is syntactically correct?

Choose the only syntactically correct attribute declaration in C#.

A

[AttributeUsage(AttributeTargets.Class, AllowMultiple = True)]
public class MultiUseAttribute : Attribute {}

B

[AttributeUsage(AttributeTargets.Class, AllowMultiple = "true")]
public class MultiUseAttribute : Attribute {}

C

[AttributeUsage(AttributeTargets.Class, AllowMultiple = 1)]
public class MultiUseAttribute : Attribute {}

D

[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
public class MultiUseAttribute : Attribute {}

💡 Hint

Check the type of the AllowMultiple parameter in AttributeUsage.

AllowMultiple expects a boolean value true or false without quotes and with lowercase 'true'. Only option D uses the correct syntax.