[C言語] enum(列挙型)の使い方についてわかりやすく詳しく解説

#include <stdio.h>
// 曜日を表す列挙型の宣言
enum Day {
    Sunday,    // 0
    Monday,    // 1
    Tuesday,   // 2
    Wednesday, // 3
    Thursday,  // 4
    Friday,    // 5
    Saturday   // 6
};

#include <stdio.h>
// 月を表す列挙型の宣言と初期化
enum Month {
    January = 1,  // 1
    February,     // 2
    March,        // 3
    April,        // 4
    May,          // 5
    June,         // 6
    July,         // 7
    August,       // 8
    September,    // 9
    October,      // 10
    November,     // 11
    December      // 12
};

#include <stdio.h>
// グローバルスコープでの宣言
enum Color {
    Red,
    Green,
    Blue
};
void printColor(enum Color color) {
    // 関数内での使用
    switch (color) {
        case Red:
            printf("Red\n");
            break;
        case Green:
            printf("Green\n");
            break;
        case Blue:
            printf("Blue\n");
            break;
        default:
            printf("Unknown Color\n");
    }
}
int main() {
    enum Color myColor = Green;
    printColor(myColor); // 出力: Green
    return 0;
}

#include <stdio.h>
// 状態を表す列挙型の宣言
enum State {
    Idle,
    Running,
    Stopped
};
int main() {
    enum State currentState = Running;
    // 列挙型を使った条件分岐
    if (currentState == Idle) {
        printf("The system is idle.\n");
    } else if (currentState == Running) {
        printf("The system is running.\n");
    } else if (currentState == Stopped) {
        printf("The system is stopped.\n");
    }
    return 0;
}

#include <stdio.h>
// 操作を表す列挙型の宣言
enum Operation {
    Add,
    Subtract,
    Multiply,
    Divide
};
void performOperation(enum Operation op, int a, int b) {
    switch (op) {
        case Add:
            printf("Result: %d\n", a + b);
            break;
        case Subtract:
            printf("Result: %d\n", a - b);
            break;
        case Multiply:
            printf("Result: %d\n", a * b);
            break;
        case Divide:
            if (b != 0) {
                printf("Result: %d\n", a / b);
            } else {
                printf("Error: Division by zero\n");
            }
            break;
        default:
            printf("Unknown operation\n");
    }
}
int main() {
    performOperation(Add, 10, 5); // 出力: Result: 15
    performOperation(Divide, 10, 0); // 出力: Error: Division by zero
    return 0;
}

#include <stdio.h>
// エラーコードを表す列挙型の宣言
enum ErrorCode {
    Success,
    FileNotFound,
    AccessDenied,
    UnknownError
};
void handleError(enum ErrorCode error) {
    switch (error) {
        case Success:
            printf("Operation completed successfully.\n");
            break;
        case FileNotFound:
            printf("Error: File not found.\n");
            break;
        case AccessDenied:
            printf("Error: Access denied.\n");
            break;
        case UnknownError:
            printf("Error: Unknown error occurred.\n");
            break;
        default:
            printf("Error: Unrecognized error code.\n");
    }
}
int main() {
    handleError(FileNotFound); // 出力: Error: File not found.
    handleError(Success); // 出力: Operation completed successfully.
    return 0;
}

#include <stdio.h>
// 列挙型の宣言
enum Status {
    Active = 1,
    Inactive = 0
};
int main() {
    enum Status currentStatus = Active;
    int statusValue = currentStatus; // 列挙型から整数型への変換
    printf("Status value: %d\n", statusValue); // 出力: Status value: 1
    return 0;
}

#include <stdio.h>
// 列挙型の宣言
enum Fruit {
    Apple,
    Banana
};
enum Color {
    Red,
    Green,
    Blue
};
int main() {
    enum Fruit myFruit = Apple;
    enum Color myColor = Red;
    printf("Fruit: %d, Color: %d\n", myFruit, myColor); // 出力: Fruit: 0, Color: 0
    return 0;
}

#include <stdio.h>
// システム状態を表す列挙型の宣言
enum SystemState {
    Initializing,
    Running,
    Paused,
    Terminated
};
void printSystemState(enum SystemState state) {
    switch (state) {
        case Initializing:
            printf("System is initializing.\n");
            break;
        case Running:
            printf("System is running.\n");
            break;
        case Paused:
            printf("System is paused.\n");
            break;
        case Terminated:
            printf("System is terminated.\n");
            break;
        default:
            printf("Unknown state.\n");
    }
}
int main() {
    enum SystemState currentState = Running;
    printSystemState(currentState); // 出力: System is running.
    return 0;
}

#include <stdio.h>
// フラグを表す列挙型の宣言
enum FilePermissions {
    Read = 1 << 0,  // 0001
    Write = 1 << 1, // 0010
    Execute = 1 << 2 // 0100
};
void checkPermissions(int permissions) {
    if (permissions & Read) {
        printf("Read permission granted.\n");
    }
    if (permissions & Write) {
        printf("Write permission granted.\n");
    }
    if (permissions & Execute) {
        printf("Execute permission granted.\n");
    }
}
int main() {
    int myPermissions = Read | Execute;
    checkPermissions(myPermissions); 
    // 出力:
    // Read permission granted.
    // Execute permission granted.
    return 0;
}

#include <stdio.h>
// プロトコルコマンドを表す列挙型の宣言
enum ProtocolCommand {
    Connect,
    Disconnect,
    SendData,
    ReceiveData
};
void executeCommand(enum ProtocolCommand command) {
    switch (command) {
        case Connect:
            printf("Executing Connect command.\n");
            break;
        case Disconnect:
            printf("Executing Disconnect command.\n");
            break;
        case SendData:
            printf("Executing SendData command.\n");
            break;
        case ReceiveData:
            printf("Executing ReceiveData command.\n");
            break;
        default:
            printf("Unknown command.\n");
    }
}
int main() {
    executeCommand(SendData); // 出力: Executing SendData command.
    return 0;
}