Flags attribute and bitwise enums in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combined flags with bitwise OR

What is the output of this C# code using a Flags enum?

C Sharp (C#)

using System;

[Flags]
public enum Permissions
{
    None = 0,
    Read = 1,
    Write = 2,
    Execute = 4
}

class Program
{
    static void Main()
    {
        Permissions userPerms = Permissions.Read | Permissions.Write;
        Console.WriteLine(userPerms);
    }
}

A "Read"

B "Read, Write"

C "3"

D "Write"

💡 Hint

Look at how Flags attribute changes enum ToString output when combined with bitwise OR.

The Flags attribute allows combined enum values to be displayed as a comma-separated list of names. Here, Read (1) OR Write (2) equals 3, but ToString shows "Read, Write".

❓ Predict Output

intermediate

Check if a flag is set using bitwise AND

What will this program print when checking if the Write flag is set?

C Sharp (C#)

using System;

[Flags]
public enum Access
{
    None = 0,
    Read = 1,
    Write = 2,
    Delete = 4
}

class Program
{
    static void Main()
    {
        Access rights = Access.Read | Access.Delete;
        bool canWrite = (rights & Access.Write) == Access.Write;
        Console.WriteLine(canWrite);
    }
}

A Runtime exception

B True

C Compile error

D False

💡 Hint

Bitwise AND with a flag returns the flag if set, otherwise zero.

The rights variable has Read and Delete flags set, but not Write. So (rights & Access.Write) equals 0, which is not equal to Access.Write (2), so canWrite is false.

❓ Predict Output

advanced

Output of combined flags with overlapping values

What is the output of this code with overlapping enum values and Flags attribute?

C Sharp (C#)

using System;

[Flags]
public enum Options
{
    None = 0,
    Alpha = 1,
    Beta = 2,
    Gamma = 3
}

class Program
{
    static void Main()
    {
        Options opt = Options.Alpha | Options.Beta;
        Console.WriteLine(opt);
    }
}

A "Gamma"

B "Alpha"

C "Alpha, Beta"

D "3"

💡 Hint

Check the numeric values and how bitwise OR combines them.

Alpha is 1, Beta is 2, so Alpha | Beta is 3. Gamma is also 3. The Flags attribute ToString returns the exact matching name if found, so it prints "Gamma".

❓ Predict Output

advanced

Count how many flags are set in a Flags enum

What is the output of this program that counts set flags?

C Sharp (C#)

using System;

[Flags]
public enum Features
{
    None = 0,
    FeatureA = 1,
    FeatureB = 2,
    FeatureC = 4,
    FeatureD = 8
}

class Program
{
    static void Main()
    {
        Features enabled = Features.FeatureA | Features.FeatureC | Features.FeatureD;
        int count = 0;
        foreach (Features f in Enum.GetValues(typeof(Features)))
        {
            if (f != Features.None && (enabled & f) == f)
                count++;
        }
        Console.WriteLine(count);
    }
}

A 3

B 4

C 2

D 1

💡 Hint

Count how many individual flags are included in the combined value.

FeatureA, FeatureC, and FeatureD are set, so count is 3.

🧠 Conceptual

expert

Why use powers of two in Flags enums?

Why must each flag in a Flags enum have a value that is a power of two?

A To make the enum values easier to read as decimal numbers

B To prevent the enum from being used in switch statements

C To ensure each flag represents a unique bit so they can be combined without overlap

D To allow the enum to be sorted alphabetically by value

💡 Hint

Think about how bits combine in binary when using bitwise OR.

Using powers of two ensures each flag corresponds to a unique bit position. This allows combining flags with bitwise OR without losing information or causing overlap.