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C Enums

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In C programming, an enumeration (enum) is a user-defined data type that consists of named integer constants. Enums make programs more readable, maintainable, and self-explanatory, as you can use meaningful names instead of numeric values. They are commonly used for representing states, categories, options, or any list of discrete values.

Enums provide a clear way to work with sets of related constants and help reduce errors from using arbitrary numbers in your code. They are particularly useful when multiple parts of a program need to agree on a set of fixed values, such as days of the week, levels of priority, or status codes.

What is an Enum?

To define an enumeration, use the enum keyword followed by an enum tag and a list of constant names:

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

  • Weekday is the enum tag.

  • Constants Sunday to Saturday are automatically assigned integer values starting from 0.

  • The underlying type of enum constants is int.

By using descriptive names like Sunday or Monday, the program becomes easier to read and understand compared to using arbitrary numbers like 0 or 1.

Declaring Enum Variables

After defining an enum, declare variables like this:

enum Weekday today, tomorrow;

  • Enum variables can hold any value defined in the enumeration.

  • You can assign a value during declaration:

enum Weekday today = Monday;

  • Enum variables are typically used in conditional statements, loops, and switch cases to make decisions based on discrete options.

Assigning Custom Values

You can assign specific integer values to enum constants:

enum Month {
    January = 1,
    February,
    March,
    April = 10,
    May,
    June
};

  • February automatically becomes 2, March becomes 3.

  • April is explicitly 10, so May becomes 11 and June becomes 12.

  • Custom values are helpful when enum constants need to correspond to real-world numbers, like month numbers or error codes.

Accessing Enum Values

Enum constants can be used in assignments, comparisons, and printing:

#include <stdio.h>

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

int main() {
    enum Weekday today = Wednesday;

    if (today == Wednesday) {
        printf("Midweek day!\n");
    }

    printf("Numeric value of Wednesday: %d\n", today);
    return 0;
}

  • Enum constants improve code readability instead of using numeric values like 3.

  • Using enums reduces the chances of accidental errors from using incorrect numbers.

Using Enums in Switch Statements

Enums are commonly used with switch statements for clear decision-making:

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

enum Weekday today = Friday;

switch(today) {
    case Sunday: printf("Rest day\n"); break;
    case Friday: printf("Last working day\n"); break;
    default: printf("Regular day\n"); break;
}

  • Makes logic easier to understand compared to using numbers directly.

  • Helps avoid magic numbers, which are numeric literals without explanation.

Enum and Arrays

Enums can also be used to index arrays, which makes programs more organized:

enum Color { Red, Green, Blue };
const char *colorNames[] = { "Red", "Green", "Blue" };

enum Color c = Green;
printf("Selected color: %s\n", colorNames[c]);

  • Enum constants correspond to array indices, making it easy to map names to values.

  • Useful in menu systems, option selectors, and game programming, where options are predefined.

Enum with Typedef

typedef can simplify enum declarations:

typedef enum {
    Low,
    Medium,
    High
} Priority;

Priority p = Medium;

  • You don’t need to write enum Priority every time.

  • Makes code shorter, more readable, and maintainable, especially in large programs.

Enum in Real-World Programs

Enums are often used in state machines, error handling, and configuration settings:

typedef enum {
    ERROR_NONE,
    ERROR_MEMORY,
    ERROR_IO,
    ERROR_TIMEOUT
} ErrorCode;

ErrorCode code = ERROR_IO;

if(code == ERROR_IO) {
    printf("Input/output error occurred.\n");
}

  • Enum constants give meaningful names to error codes instead of using numbers like 1 or 2.

  • This approach improves debugging and maintenance, making programs less error-prone.

Practical Example: Menu System

#include <stdio.h>

typedef enum {
    OptionNew = 1,
    OptionOpen,
    OptionSave,
    OptionExit
} MenuOption;

int main() {
    MenuOption choice;
    printf("Enter choice (1-New, 2-Open, 3-Save, 4-Exit): ");
    scanf("%d", &choice);

    switch(choice) {
        case OptionNew: printf("Creating new file...\n"); break;
        case OptionOpen: printf("Opening file...\n"); break;
        case OptionSave: printf("Saving file...\n"); break;
        case OptionExit: printf("Exiting...\n"); break;
        default: printf("Invalid option\n");
    }

    return 0;
}

  • Demonstrates typedef enum, user input, and switch-case usage.

  • Enum improves readability by using descriptive names instead of numbers.

Best Practices

  1. Use enums to represent fixed sets of related constants.

  2. Provide meaningful names for constants.

  3. Use typedef for cleaner syntax.

  4. Combine enums with switch statements and arrays for structured programming.

  5. Avoid using enums for values that change at runtime—they are intended for fixed constants.

Summary of the Tutorial

Enums in C are user-defined constants that make programs readable, organized, and maintainable. They are ideal for representing options, states, error codes, days of the week, or configuration settings. By combining enums with typedef, switch statements, and arrays, programmers can write clean, efficient, and understandable code. Enums are especially useful in large-scale or complex programs, where using numeric literals would be confusing and error-prone.

Practice Questions

  1. Define an enum Weekday with constants for all seven days. Write a program to input a day number (0–6) and print its name.

  2. Create an enum Month with all months and assign January = 1. Write a program to input a number (1–12) and display the corresponding month.

  3. Define an enum LogLevel with values DEBUG, INFO, WARNING, ERROR. Write a program to display messages based on the log level input by the user.

  4. Write a program using an enum TrafficLight with constants Red, Yellow, Green and print instructions for each color using a switch statement.

  5. Define a typedef enum Priority with values Low, Medium, High. Write a program that inputs a priority level and prints a corresponding message.

  6. Create an enum MenuOption for options New, Open, Save, Exit. Write a program that takes user input and performs the appropriate action.

  7. Write a program using an enum ErrorCode with constants None, Memory, IO, Timeout. Display an error message depending on the selected enum value.

  8. Define an enum Direction with values North, East, South, West. Input a direction from the user and display its opposite direction.

  9. Create an array of strings corresponding to an enum Color with constants Red, Green, Blue. Write a program to input a color enum and display its string name.

  10. Define an enum Season with constants Spring, Summer, Autumn, Winter. Input a season and print typical activities for that season using a switch statement.

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