Enum usage in C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an enum in C?

An enum in C is a way to name a set of integer constants. It helps make code easier to read by giving meaningful names to numbers.

beginner

How do you define an enum for days of the week in C?

You write:

enum Day { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

This creates names for numbers starting at 0.

intermediate

Can you assign specific numbers to enum members?

Yes. You can set values like

enum Color { Red = 1, Green = 5, Blue = 10 };

. Members without assigned values get the next number after the previous one.

beginner

How do you use an enum variable in C?

Declare a variable with the enum type, like

enum Day today;

. Then assign a value:

today = Monday;

. It stores the integer for Monday.

beginner

What is the default starting value of the first enum member if not assigned?

The first enum member starts at 0 by default. Each next member increases by 1 unless specified otherwise.

What value does the first member of an enum have if not explicitly assigned?

A -1

B 1

C 0

D Undefined

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

How do you declare an enum variable named color of type enum Color?

A enum Color color;

B Color enum color;

C int color;

D var color = enum Color;

The correct syntax is enum Color color; to declare a variable of enum type.

If you define enum Fruit { Apple = 3, Banana, Cherry };, what is the value of Cherry?

A 3

B 5

C Undefined

D 4

Cherry gets the next integer after Banana, which is 5.

Which of these is a benefit of using enums?

A Automatically creates functions

B Slows down the program

C Allows floating point values

D Makes code easier to read by using names instead of numbers

Enums improve code readability by replacing numbers with meaningful names.

Can enum members have duplicate values?

A Yes, but it is not recommended

B No, it causes a compile error

C Only if they are consecutive

D Only if they are the first two members

Enum members can have the same value, but it can cause confusion and is usually avoided.

Explain what an enum is and how it helps in C programming.

Think about how enums replace numbers with names.

Describe how to assign specific values to enum members and what happens to members without assigned values.

Consider how numbering works inside enums.

Practice

1. What is the main purpose of using enum in C programming?

easy

A. To give names to integer constants for better code readability

B. To create floating-point variables

C. To define functions

D. To allocate memory dynamically

Solution

1. Step 1: Understand enum usage

   An enum groups related integer constants under meaningful names.

2. Step 2: Identify the purpose

   This helps make code easier to read and maintain by replacing numbers with names.

3. Final Answer:

   To give names to integer constants for better code readability -> Option A

4. Quick Check:

   Enum = Named integer constants [OK]

Hint: Enums name numbers to improve code clarity [OK]

Common Mistakes:

• Thinking enums create variables or functions
• Confusing enums with dynamic memory
• Assuming enums hold floating-point values

2. Which of the following is the correct syntax to declare an enum named Color with values RED, GREEN, and BLUE?

easy

A. enum Color: RED, GREEN, BLUE;

B. enum Color = { RED, GREEN, BLUE };

C. enum Color { RED, GREEN, BLUE };

D. enum Color ( RED, GREEN, BLUE );

Solution

1. Step 1: Recall enum declaration syntax

   In C, enums are declared using the keyword enum, followed by the name and braces with values separated by commas.

2. Step 2: Check each option

   enum Color { RED, GREEN, BLUE }; uses correct syntax: enum Color { RED, GREEN, BLUE };. Others use invalid symbols or assignment.

3. Final Answer:

   enum Color { RED, GREEN, BLUE }; -> Option C

4. Quick Check:

   Correct enum syntax uses braces and commas [OK]

Hint: Use braces {} and commas for enum values [OK]

Common Mistakes:

• Using '=' instead of braces
• Using parentheses instead of braces
• Using colon ':' which is invalid in C enums

3. What will be the output of this C code?

enum Day { SUN, MON, TUE = 5, WED, THU };
#include 
int main() {
    printf("%d %d %d %d %d", SUN, MON, TUE, WED, THU);
    return 0;
}

medium

A. 1 2 5 6 7

B. 5 6 7 8 9

C. 0 1 2 3 4

D. 0 1 5 6 7

Solution

1. Step 1: Understand enum value assignment

   By default, enums start at 0 and increase by 1. Here, SUN=0, MON=1. TUE is explicitly set to 5.

2. Step 2: Calculate following values

   After TUE=5, WED becomes 6, and THU becomes 7 automatically.

3. Final Answer:

   0 1 5 6 7 -> Option D

4. Quick Check:

   Explicit enum values override counting [OK]

Hint: Explicit enum values reset counting from that point [OK]

Common Mistakes:

• Assuming all values auto-increment ignoring explicit assignments
• Starting enum values at 1 by default
• Confusing enum names with strings

4. Identify the error in this enum declaration:

enum Status {
    OK = 1,
    ERROR,
    WARNING = "3"
};

medium

A. Missing semicolon after enum declaration

B. Enum values must be integers, not strings

C. Enum names cannot be uppercase

D. ERROR cannot follow OK without explicit value

Solution

1. Step 1: Check enum value types

   Enum values in C must be integer constants. Here, WARNING is assigned a string "3", which is invalid.

2. Step 2: Verify other syntax

   Semicolon is present, uppercase names are allowed, and ERROR can auto-increment from OK=1.

3. Final Answer:

   Enum values must be integers, not strings -> Option B

4. Quick Check:

   Enum values = integers only [OK]

Hint: Enum values must be integer constants [OK]

Common Mistakes:

• Assigning strings to enum values
• Thinking enum names must be lowercase
• Forgetting semicolon after enum

5. Given this enum and code snippet, what is the output?

enum Flags { FLAG_A = 1 << 0, FLAG_B = 1 << 1, FLAG_C = 1 << 2 };
#include 
int main() {
    int combined = FLAG_A | FLAG_C;
    if (combined & FLAG_B) {
        printf("Flag B set\n");
    } else {
        printf("Flag B not set\n");
    }
    return 0;
}

hard

A. Flag B not set

B. Flag B set

C. Compilation error

D. Flag A and C set

Solution

1. Step 1: Understand bitwise enum values

   FLAG_A = 1 (binary 001), FLAG_B = 2 (010), FLAG_C = 4 (100). Combined = FLAG_A | FLAG_C = 1 | 4 = 5 (binary 101).

2. Step 2: Check if FLAG_B is set in combined

   combined & FLAG_B = 5 & 2 = 0 (binary 101 & 010 = 000), so FLAG_B is not set.

3. Final Answer:

   Flag B not set -> Option A

4. Quick Check:

   Bitwise AND zero means flag not set [OK]

Hint: Use bitwise AND to check if flag is set [OK]

Common Mistakes:

• Assuming combined flags include all bits
• Confusing bitwise OR and AND
• Expecting compilation error due to bit shifts