Examples of flag usage in C language

Usage of flag in C language: Program control: represents true/false status, used to control program flow based on conditions. Status indicator: Indicates a specific status, such as whether it is registered. Error handling: Used to handle errors, such as returning an error code when a file fails to open. Parameter passing: Indicates optional parameters, used to modify function behavior.

Usage examples of flag in C language

flag is a widely used variable type in C language, representing A Boolean value (true or false). It is often used to control program flow or indicate a specific status. Here are some common usage examples of flag:

As a program control

<code class="c">int main() {
    int flag = 0; // 初始化为假

    // 当满足某个条件时，将 flag 设置为真
    if (condition) {
        flag = 1;
    }

    // 根据 flag 的值执行不同的操作
    if (flag) {
        // 条件为真时执行的代码
    } else {
        // 条件为假时执行的代码
    }

    return 0;
}</code>

As a status indicator

<code class="c">struct student {
    int id;
    char name[50];
    int enrolled; // 0: 未注册，1: 已注册
};

void register_student(struct student *student) {
    student->enrolled = 1;
}

int is_student_enrolled(struct student *student) {
    return student->enrolled;
}</code>

Handling as error

<code class="c">int open_file(const char *filename) {
    FILE *file;

    file = fopen(filename, "r");
    if (!file) {
        return -1; // 返回错误代码
    }

    return file;
}

int main() {
    FILE *file = open_file("myfile.txt");
    if (file == -1) {
        // 处理文件打开错误
    }

    // 使用 file 指针读取文件内容

    fclose(file);
    return 0;
}</code>

Passed as parameter

<code class="c">void print_array(int arr[], int size, int reverse) {
    if (reverse) {
        for (int i = size - 1; i >= 0; i--) {
            printf("%d ", arr[i]);
        }
    } else {
        for (int i = 0; i < size; i++) {
            printf("%d ", arr[i]);
        }
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);

    print_array(arr, size, 0); // 正序打印数组
    print_array(arr, size, 1); // 倒序打印数组

    return 0;
}</code>

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