Enum declaration - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enum variable assignment

What is the output of this C code?

C

#include <stdio.h>

enum Color { RED, GREEN, BLUE };

int main() {
    enum Color c = GREEN;
    printf("%d", c);
    return 0;
}

A 0

B 1

C Compilation error

D 2

💡 Hint

Remember that enum values start from 0 by default.

The enum Color assigns RED=0, GREEN=1, BLUE=2. So printing GREEN prints 1.

❓ Predict Output

intermediate

Enum with custom values output

What will this program print?

C

#include <stdio.h>

enum Status { OK = 5, WARNING = 10, ERROR = 15 };

int main() {
    enum Status s = WARNING;
    printf("%d", s);
    return 0;
}

A 0

B 5

C 15

D 10

💡 Hint

Check the assigned values for each enum member.

The enum WARNING is assigned the value 10 explicitly, so printing it outputs 10.

🔧 Debug

advanced

Identify the error in enum declaration

What error will this code produce?

C

enum Days { MON, TUE, WED = "3", THU, FRI };

int main() {
    enum Days today = WED;
    return 0;
}

A No error, compiles fine

B Warning: implicit conversion from string to int

C TypeError: enum member must be integer constant

D SyntaxError: enum member cannot be a string

💡 Hint

Enum values must be integer constants.

Enum members must be integer constants. Assigning a string literal causes a type error during compilation.

❓ Predict Output

advanced

Enum auto-increment behavior

What is the output of this program?

C

#include <stdio.h>

enum Numbers { ONE = 1, TWO, FIVE = 5, SIX };

int main() {
    printf("%d %d %d %d", ONE, TWO, FIVE, SIX);
    return 0;
}

A 1 2 5 6

B 1 1 5 6

C 1 2 5 5

D 1 2 6 7

💡 Hint

Enum values auto-increment from the previous value.

ONE is 1, TWO auto-increments to 2, FIVE is explicitly 5, SIX auto-increments to 6.

🧠 Conceptual

expert

Number of items in enum

How many items are in this enum?

C

enum Letters { A = 3, B, C = 7, D, E };

A 5

B 4

C 3

D 6

💡 Hint

Count all declared enum members regardless of their values.

The enum declares five members: A, B, C, D, and E.

Practice

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

easy

A. To declare a function prototype

B. To give names to a set of integer constants for better code readability

C. To create a new data type for floating-point numbers

D. To allocate memory dynamically

Solution

1. Step 1: Understand enum usage

   An enum is used to assign names to integer constants, making code easier to read and maintain.

2. Step 2: Compare other options

   Other options describe unrelated concepts: function prototypes, floating-point types, and memory allocation.

3. Final Answer:

   To give names to a set of integer constants for better code readability -> Option B

4. Quick Check:

   Enum = Named integer constants [OK]

Hint: Enums name numbers to make code clearer [OK]

Common Mistakes:

• Confusing enums with structs or unions
• Thinking enums allocate memory dynamically
• Assuming enums are for floating-point types

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

   The correct syntax uses curly braces to list values after the enum name without assignment or colons.

2. Step 2: Check each option

   enum Color { RED, GREEN, BLUE }; uses correct syntax: enum Color { RED, GREEN, BLUE };. Others use invalid symbols like '=', '(', or ':'.

3. Final Answer:

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

4. Quick Check:

   Enum syntax = enum Name { values } [OK]

Hint: Use curly braces and no equals sign in enum declaration [OK]

Common Mistakes:

• Using '=' instead of braces
• Using parentheses instead of braces
• Using colons after enum name

3. What will be the output of the following 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. 0 1 5 5 5

B. 0 1 2 3 4

C. 1 2 5 6 7

D. 0 1 5 6 7

Solution

1. Step 1: Understand enum value assignment

   By default, enum values start at 0 and increment 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 value sets next values incrementally [OK]

Hint: Explicit enum value resets counting from that number [OK]

Common Mistakes:

• Assuming all values increment from zero ignoring explicit assignment
• Thinking WED and THU have same value as TUE
• Starting enum values from 1 by default

4. Identify the error in the following enum declaration:

enum Status {
    OK = 1,
    ERROR,
    WARNING = "2"
};

medium

A. ERROR must be assigned a value explicitly

B. Missing semicolon after enum declaration

C. Enum values must be integers, not strings

D. Enum names cannot be uppercase

Solution

1. Step 1: Check enum value types

   Enum values must be integer constants. Assigning a string like "2" is invalid.

2. Step 2: Verify other parts

   Semicolon is present, uppercase names are allowed, and ERROR can be auto-assigned after OK=1.

3. Final Answer:

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

4. Quick Check:

   Enum values = integers only [OK]

Hint: Enum values must be integers, not strings [OK]

Common Mistakes:

• Using string literals as enum values
• Forgetting semicolon after enum
• Thinking enum names must be lowercase

5. Given the enum declaration:

enum Flags { FLAG_A = 1 << 0, FLAG_B = 1 << 1, FLAG_C = 1 << 2 };

int flags = FLAG_A | FLAG_C;

Which expression correctly checks if FLAG_B is set in flags?

hard

A. (flags & FLAG_B) != 0

B. (flags | FLAG_B) == 0

C. (flags & FLAG_B) == FLAG_B + 1

D. (flags ^ FLAG_B) == 0

Solution

1. Step 1: Understand bitwise flag checking

   To check if a flag is set, use bitwise AND and compare to zero.

2. Step 2: Analyze each option

   (flags & FLAG_B) != 0 correctly checks if FLAG_B bit is set by (flags & FLAG_B) != 0. Others use incorrect bitwise operations or comparisons.

3. Final Answer:

   (flags & FLAG_B) != 0 -> Option A

4. Quick Check:

   Bitwise AND with flag and compare to zero [OK]

Hint: Use bitwise AND and compare to zero to check flags [OK]

Common Mistakes:

• Using bitwise OR instead of AND for checking
• Comparing to wrong values
• Using XOR to check flags