用C语言设计单项选择题标准化考试系统设计代码 （1）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） （2）试题录入：可随时增加试题到试题库中 （3）试题的修改和删除 （4）试题抽取：每次从试题库中可以随机抽出N道题且不重复（N由键盘输入） （5）答题：用户可实现输入自己的答案 （6）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。

以下是一个简单的单项选择题标准化考试系统设计代码，使用了C语言和文件操作：

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

#define MAX_QUESTIONS 1000
#define MAX_QUESTION_LEN 100
#define MAX_ANSWER_LEN 20

struct question {
    char prompt[MAX_QUESTION_LEN];
    char answer[4][MAX_ANSWER_LEN];
    int correct_answer;
};

int num_questions = 0;
struct question questions[MAX_QUESTIONS];

void load_questions() {
    FILE *file = fopen("questions.txt", "r");
    if (file == NULL) {
        printf("Cannot open questions file.\n");
        return;
    }
    while (!feof(file) && num_questions < MAX_QUESTIONS) {
        struct question *q = &questions[num_questions];
        fgets(q->prompt, MAX_QUESTION_LEN, file);
        for (int i = 0; i < 4; i++) {
            fgets(q->answer[i], MAX_ANSWER_LEN, file);
        }
        fscanf(file, "%d\n", &q->correct_answer);
        num_questions++;
    }
    fclose(file);
}

void save_questions() {
    FILE *file = fopen("questions.txt", "w");
    if (file == NULL) {
        printf("Cannot open questions file.\n");
        return;
    }
    for (int i = 0; i < num_questions; i++) {
        struct question *q = &questions[i];
        fprintf(file, "%s", q->prompt);
        for (int j = 0; j < 4; j++) {
            fprintf(file, "%s", q->answer[j]);
        }
        fprintf(file, "%d\n", q->correct_answer);
    }
    fclose(file);
}

void add_question() {
    if (num_questions >= MAX_QUESTIONS) {
        printf("Cannot add more questions.\n");
        return;
    }
    struct question *q = &questions[num_questions];
    printf("Enter question prompt:\n");
    fgets(q->prompt, MAX_QUESTION_LEN, stdin);
    for (int i = 0; i < 4; i++) {
        printf("Enter answer %d:\n", i + 1);
        fgets(q->answer[i], MAX_ANSWER_LEN, stdin);
    }
    printf("Enter correct answer (1-4):\n");
    scanf("%d", &q->correct_answer);
    getchar(); // consume newline
    num_questions++;
}

void modify_question() {
    printf("Enter question number to modify (1-%d):\n", num_questions);
    int n;
    scanf("%d", &n);
    if (n < 1 || n > num_questions) {
        printf("Invalid question number.\n");
        return;
    }
    struct question *q = &questions[n - 1];
    printf("Current prompt: %s", q->prompt);
    printf("Enter new prompt (or press enter to keep current):\n");
    fgets(q->prompt, MAX_QUESTION_LEN, stdin);
    for (int i = 0; i < 4; i++) {
        printf("Current answer %d: %s", i + 1, q->answer[i]);
        printf("Enter new answer %d (or press enter to keep current):\n", i + 1);
        fgets(q->answer[i], MAX_ANSWER_LEN, stdin);
    }
    printf("Current correct answer: %d\n", q->correct_answer);
    printf("Enter new correct answer (1-4, or 0 to keep current):\n");
    int new_correct_answer;
    scanf("%d", &new_correct_answer);
    if (new_correct_answer >= 1 && new_correct_answer <= 4) {
        q->correct_answer = new_correct_answer;
    }
    getchar(); // consume newline
}

void delete_question() {
    printf("Enter question number to delete (1-%d):\n", num_questions);
    int n;
    scanf("%d", &n);
    if (n < 1 || n > num_questions) {
        printf("Invalid question number.\n");
        return;
    }
    for (int i = n - 1; i < num_questions - 1; i++) {
        questions[i] = questions[i + 1];
    }
    num_questions--;
}

void shuffle_questions() {
    srand(time(NULL));
    for (int i = 0; i < num_questions; i++) {
        int j = rand() % num_questions;
        struct question temp = questions[i];
        questions[i] = questions[j];
        questions[j] = temp;
    }
}

void take_test() {
    int num_questions_to_ask;
    printf("Enter number of questions to ask:\n");
    scanf("%d", &num_questions_to_ask);
    if (num_questions_to_ask < 1 || num_questions_to_ask > num_questions) {
        printf("Invalid number of questions.\n");
        return;
    }
    shuffle_questions();
    int score = 0;
    for (int i = 0; i < num_questions_to_ask; i++) {
        struct question *q = &questions[i];
        printf("%d. %s", i + 1, q->prompt);
        for (int j = 0; j < 4; j++) {
            printf("%d. %s", j + 1, q->answer[j]);
        }
        int answer;
        scanf("%d", &answer);
        if (answer == q->correct_answer) {
            score++;
        }
        getchar(); // consume newline
    }
    printf("You got %d out of %d questions correct.\n", score, num_questions_to_ask);
}

int main() {
    load_questions();
    while (1) {
        printf("Enter a command:\n");
        printf("1. Add question\n");
        printf("2. Modify question\n");
        printf("3. Delete question\n");
        printf("4. Take test\n");
        printf("5. Quit\n");
        int choice;
        scanf("%d", &choice);
        getchar(); // consume newline
        switch (choice) {
            case 1:
                add_question();
                save_questions();
                break;
            case 2:
                modify_question();
                save_questions();
                break;
            case 3:
                delete_question();
                save_questions();
                break;
            case 4:
                take_test();
                break;
            case 5:
                return 0;
            default:
                printf("Invalid command.\n");
        }
    }
}

代码中使用了一个结构体 `question` 来保存每个试题的题干、备选答案和标准答案，以及一个数组 `questions` 来保存所有试题。在程序启动时，从文件中加载试题库；在程序运行时，用户可以添加、修改、删除试题，或者进行答题，程序会自动判卷并给出成绩。在抽取试题时，程序会随机打乱试题库的顺序，然后从中选择指定数量的试题。