Underlying numeric values in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are underlying numeric values in C# enums?

Underlying numeric values are the integer values automatically or explicitly assigned to each enum member. By default, they start at 0 and increase by 1 for each member.

beginner

How can you specify a custom underlying numeric value for an enum member in C#?

You assign a value directly to the enum member, for example: enum Days { Sunday = 1, Monday = 2 }.

beginner

What is the default underlying type of an enum in C#?

The default underlying type of an enum in C# is int.

intermediate

Can you change the underlying type of an enum in C#? If yes, how?

Yes, you can specify a different integral type like byte, short, long by declaring it after the enum name, e.g., enum Colors : byte { Red, Green }.

beginner

How do you get the underlying numeric value of an enum member in C#?

You can cast the enum member to its underlying type, for example: int value = (int)Days.Monday;.

What is the default underlying numeric value of the first enum member if not specified?

A 0

B 1

C -1

D Depends on the enum

By default, the first enum member has the underlying value 0.

How do you specify an enum with an underlying type of byte?

A enum Colors(byte) { Red, Green }

B enum Colors : byte { Red, Green }

C enum Colors { Red = byte, Green = byte }

D enum Colors { byte Red, byte Green }

The syntax to specify the underlying type is enum Name : type { ... }.

What happens if you assign the same numeric value to two enum members?

A It causes a compile error

B The second member gets incremented automatically

C Both members share the same underlying value

D The enum becomes invalid

Enum members can share the same underlying value without error.

How do you retrieve the numeric value of an enum member in C#?

A Use a cast like (int)EnumMember

B Use Enum.GetValue() method

C Use Enum.ToString()

D Use Enum.Parse()

Casting the enum member to its underlying type returns its numeric value.

Which of these is NOT a valid underlying type for an enum in C#?

A int

B byte

C long

D string

Enums can only have integral underlying types, not string.

Explain what underlying numeric values are in C# enums and how they are assigned.

Think about how enum members get their numbers.

Describe how to change the underlying type of an enum and why you might want to do that.

Look at the enum declaration syntax.

Practice

1. What is the underlying numeric value of an enum member in C# if not explicitly set?

easy

A. It starts at 0 and increments by 1 for each member

B. It is always 1 for all members

C. It is a random number assigned by the compiler

D. It must be manually assigned for each member

Solution

1. Step 1: Understand default enum numbering

   By default, C# assigns the first enum member the value 0.

2. Step 2: Check subsequent members

   Each following member increments by 1 automatically unless explicitly set.

3. Final Answer:

   It starts at 0 and increments by 1 for each member -> Option A

4. Quick Check:

   Default enum values start at 0 and increment [OK]

Hint: Remember enums start at zero unless you say otherwise [OK]

Common Mistakes:

• Thinking enums start at 1 by default
• Assuming enum values are random
• Believing manual assignment is always required

2. Which of the following is the correct way to get the numeric value of an enum member Day.Monday in C#?

easy

A. int value = Convert.ToInt32(Day.Monday.ToString());

B. int value = Day.Monday.ToInt();

C. int value = Day.Monday.Value;

D. int value = (int)Day.Monday;

Solution

1. Step 1: Recall casting enum to int

   In C#, you get the numeric value by casting the enum member to int using (int).

2. Step 2: Check other options

   Enums have no ToInt() method or Value property; Convert.ToInt32(Day.Monday.ToString()) parses the name ("Monday") and throws FormatException.

3. Final Answer:

   int value = (int)Day.Monday; -> Option D

4. Quick Check:

   Cast enum to int with (int) [OK]

Hint: Cast enum to int with (int) to get its number [OK]

Common Mistakes:

• Using non-existent methods like ToInt()
• Trying to access a Value property
• Converting enum.ToString() to int (parses name)

3. Given the enum:

enum Color { Red = 3, Green, Blue }

What is the output of this code?

Console.WriteLine((int)Color.Green);

medium

A. 4

B. 3

C. 1

D. 0

Solution

1. Step 1: Identify explicit enum value

   Color.Red is set to 3 explicitly.

2. Step 2: Understand implicit increment

   Color.Green is next, so it gets 4 (3 + 1).

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Enum increments from explicit value [OK]

Hint: Next enum value increments by 1 from previous explicit value [OK]

Common Mistakes:

• Assuming Green is 1 by default
• Thinking Green equals Red's value
• Forgetting implicit increment after explicit value

4. What is wrong with this code snippet?

enum Status { Active = 1, Inactive = 1, Pending = 2 }

medium

A. Enum members cannot have duplicate values

B. Nothing is wrong; duplicate values are allowed

C. Enum members must be strings, not numbers

D. Enum members must be assigned sequentially starting at 0

Solution

1. Step 1: Check enum value rules

   C# allows enum members to share the same underlying numeric value.

2. Step 2: Verify other options

   Enum members can be numbers, do not need sequential values, and duplicates are allowed.

3. Final Answer:

   Nothing is wrong; duplicate values are allowed -> Option B

4. Quick Check:

   Duplicate enum values are valid in C# [OK]

Hint: Duplicate enum values are allowed in C# [OK]

Common Mistakes:

• Thinking duplicate enum values cause errors
• Believing enums must start at 0 and be sequential
• Confusing enum members with strings

5. You have this enum:

enum Level { Low = 1, Medium = 5, High = 10 }

Which code correctly checks if an integer variable score matches any enum value?

hard

A. bool isMatch = score >= (int)Level.Low && score <= (int)Level.High;

B. bool isMatch = (Level)score != null;

C. bool isMatch = Enum.IsDefined(typeof(Level), score);

D. bool isMatch = score == Level.Low || score == Level.Medium || score == Level.High;

Solution

1. Step 1: Understand Enum.IsDefined usage

   Enum.IsDefined checks if a given integer matches any enum member's underlying value.

2. Step 2: Analyze other options

   A checks range (includes invalid like 2); B casts int to enum (always succeeds) != null (always true); C direct int == enum comparisons do not compile without casting enum to int.

3. Final Answer:

   bool isMatch = Enum.IsDefined(typeof(Level), score); -> Option C

4. Quick Check:

   Use Enum.IsDefined to check valid enum values [OK]

Hint: Use Enum.IsDefined to check if int matches enum value [OK]

Common Mistakes:

• Casting int to enum without validation
• Checking range instead of exact enum values
• Comparing int directly to enum members without casting