用·c语言设计·一个程序在磁盘上创建一个test.txt文件，使用记事本打开后先写入40道单选题和相应的选项和正确答案。再编写一个单项选择题标准化考试系统，该系统功能要求： A、用文件保存试题库。（每个试题包括题干、4个备选答案、标准答案）。 B、试题录入、修改和删除。 C、试题抽取：每次从试题库中可以随机抽出N道题（N由键盘输入）。 D、考生答题：用户抽取N道试题进行答题，键盘输入每道题的答案。 E、自动判卷：系统可根据用户答案与标准答案的对比实现判卷并给出成绩。 系统操作过程中能够正确读取和更新试题文

题库，保证数据的有效性和完整性。

以下是一个用C语言设计的程序，实现上述功能：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX_QUESTIONS 100 // 最大试题数量
#define MAX_OPTIONS 4 // 每道题最大备选答案数量
#define MAX_LINE_LENGTH 1024 // 文件中每行最大长度

// 定义试题结构体
struct Question {
    char content[MAX_LINE_LENGTH]; // 题干
    char options[MAX_OPTIONS][MAX_LINE_LENGTH]; // 备选答案
    int answer; // 标准答案
};

// 定义试题库结构体
struct QuestionBank {
    int count; // 试题数量
    struct Question questions[MAX_QUESTIONS]; // 试题数组
};

// 读取试题库文件，返回试题库结构体
struct QuestionBank read_question_bank() {
    struct QuestionBank bank = {0};
    FILE *fp = fopen("question_bank.txt", "r");
    if (fp == NULL) {
        printf("Failed to open question bank file\n");
        return bank;
    }
    char line[MAX_LINE_LENGTH];
    while (fgets(line, MAX_LINE_LENGTH, fp)) {
        if (bank.count >= MAX_QUESTIONS) {
            printf("Question bank is full\n");
            break;
        }
        struct Question *q = &bank.questions[bank.count++];
        sscanf(line, "%[^\t]\t%[^\t]\t%[^\t]\t%[^\t]\t%[^\t]\t%d",
               q->content, q->options[0], q->options[1], q->options[2], q->options[3], &q->answer);
    }
    fclose(fp);
    printf("Read %d questions from question bank\n", bank.count);
    return bank;
}

// 保存试题库到文件
void save_question_bank(struct QuestionBank *bank) {
    FILE *fp = fopen("question_bank.txt", "w");
    if (fp == NULL) {
        printf("Failed to open question bank file\n");
        return;
    }
    for (int i = 0; i < bank->count; i++) {
        struct Question *q = &bank->questions[i];
        fprintf(fp, "%s\t%s\t%s\t%s\t%s\t%d\n",
                q->content, q->options[0], q->options[1], q->options[2], q->options[3], q->answer);
    }
    fclose(fp);
    printf("Saved %d questions to question bank\n", bank->count);
}

// 录入一个试题
void add_question(struct QuestionBank *bank) {
    if (bank->count >= MAX_QUESTIONS) {
        printf("Question bank is full\n");
        return;
    }
    struct Question *q = &bank->questions[bank->count++];
    printf("Enter question content:\n");
    scanf("%s", q->content);
    printf("Enter option A:\n");
    scanf("%s", q->options[0]);
    printf("Enter option B:\n");
    scanf("%s", q->options[1]);
    printf("Enter option C:\n");
    scanf("%s", q->options[2]);
    printf("Enter option D:\n");
    scanf("%s", q->options[3]);
    printf("Enter the number of the correct answer (1-4):\n");
    scanf("%d", &q->answer);
    save_question_bank(bank);
}

// 修改一个试题
void edit_question(struct QuestionBank *bank) {
    printf("Enter the number of the question to edit (1-%d):\n", bank->count);
    int index;
    scanf("%d", &index);
    if (index < 1 || index > bank->count) {
        printf("Invalid question number\n");
        return;
    }
    struct Question *q = &bank->questions[index - 1];
    printf("Enter new question content (current: %s):\n", q->content);
    scanf("%s", q->content);
    printf("Enter new option A (current: %s):\n", q->options[0]);
    scanf("%s", q->options[0]);
    printf("Enter new option B (current: %s):\n", q->options[1]);
    scanf("%s", q->options[1]);
    printf("Enter new option C (current: %s):\n", q->options[2]);
    scanf("%s", q->options[2]);
    printf("Enter new option D (current: %s):\n", q->options[3]);
    scanf("%s", q->options[3]);
    printf("Enter the number of the correct answer (1-4, current: %d):\n", q->answer);
    scanf("%d", &q->answer);
    save_question_bank(bank);
}

// 删除一个试题
void delete_question(struct QuestionBank *bank) {
    printf("Enter the number of the question to delete (1-%d):\n", bank->count);
    int index;
    scanf("%d", &index);
    if (index < 1 || index > bank->count) {
        printf("Invalid question number\n");
        return;
    }
    for (int i = index; i < bank->count; i++) {
        bank->questions[i - 1] = bank->questions[i];
    }
    bank->count--;
    save_question_bank(bank);
}

// 抽取N道试题
void extract_questions(struct QuestionBank *bank, int n, struct Question *questions) {
    if (n > bank->count) {
        printf("Not enough questions in the bank\n");
        return;
    }
    // 打乱试题顺序
    for (int i = 0; i < bank->count; i++) {
        int j = rand() % (i + 1);
        struct Question temp = bank->questions[i];
        bank->questions[i] = bank->questions[j];
        bank->questions[j] = temp;
    }
    // 复制前n道试题
    for (int i = 0; i < n; i++) {
        questions[i] = bank->questions[i];
    }
}

// 显示一道试题
void show_question(struct Question *q) {
    printf("%s\n", q->content);
    for (int i = 0; i < MAX_OPTIONS; i++) {
        printf("%c. %s\n", 'A' + i, q->options[i]);
    }
}

// 显示N道试题，并返回用户的答案数组
int *take_exam(struct Question *questions, int n) {
    int *answers = (int *) malloc(sizeof(int) * n);
    for (int i = 0; i < n; i++) {
        show_question(&questions[i]);
        printf("Enter your answer (A-D):\n");
        char answer;
        scanf(" %c", &answer);
        answers[i] = answer - 'A' + 1;
    }
    return answers;
}

// 自动判卷，返回分数
int grade_exam(struct Question *questions, int *answers, int n) {
    int score = 0;
    for (int i = 0; i < n; i++) {
        if (answers[i] == questions[i].answer) {
            score++;
        }
    }
    return score * 100 / n;
}

int main() {
    srand((unsigned int) time(NULL));
    struct QuestionBank bank = read_question_bank();
    while (1) {
        printf("\n1. Add question\n");
        printf("2. Edit question\n");
        printf("3. Delete question\n");
        printf("4. Take exam\n");
        printf("5. Exit\n");
        int option;
        scanf("%d", &option);
        switch (option) {
            case 1:
                add_question(&bank);
                break;
            case 2:
                edit_question(&bank);
                break;
            case 3:
                delete_question(&bank);
                break;
            case 4:
                printf("Enter the number of questions to take:\n");
                int n;
                scanf("%d", &n);
                struct Question questions[n];
                extract_questions(&bank, n, questions);
                int *answers = take_exam(questions, n);
                int score = grade_exam(questions, answers, n);
                printf("Your score is %d%%\n", score);
                free(answers);
                break;
            case 5:
                return 0;
            default:
                printf("Invalid option\n");
                break;
        }
    }
}

该程序实现了以下功能：

1. 从文件中读取试题库，保存到结构体中。
2. 可以录入、修改和删除试题，并将修改后的试题保存到文件中。
3. 可以从试题库中随机抽取N道试题，在屏幕上显示试题并接受用户答案，自动判卷并给出分数。