C语言设计一考勤系统。考勤信息记录了学生的缺课情况，它包括：缺课日期、第几节课、课程名称、学生姓名、学生学号、缺课类型（迟到、早退、请假及旷课）。系统具有以下功能： 1、 录入学生的缺课记录； 2、 修改某个学生的缺课记录； 3、 查询某个学生的缺课情况； 4、 统计某段时间内，旷课学生姓名及旷课次数，按旷课次数由多到少排序； 5、 统计某段时间内，有学生旷课的课程及旷课人次，按旷课人次由多到少排序； 6、 系统以菜单方式工作。

以下是一个基本的考勤系统的C语言实现：

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

#define MAX_STUDENTS 100
#define MAX_ABSENCES 200

typedef struct {
    int day;
    int period;
    char course[50];
    char name[50];
    char id[20];
    char type[10];
} Absence;

typedef struct {
    char name[50];
    char id[20];
    int num_absences;
    Absence absences[MAX_ABSENCES];
} Student;

Student students[MAX_STUDENTS];
int num_students = 0;

void add_absence() {
    printf("Enter absence information:\n");
    Absence absence;
    printf("Day: ");
    scanf("%d", &absence.day);
    printf("Period: ");
    scanf("%d", &absence.period);
    printf("Course: ");
    scanf("%s", absence.course);
    printf("Name: ");
    scanf("%s", absence.name);
    printf("ID: ");
    scanf("%s", absence.id);
    printf("Type (late, early, leave, absent): ");
    scanf("%s", absence.type);
    
    // Find the student and add the absence to their record
    int i;
    for (i = 0; i < num_students; i++) {
        if (strcmp(students[i].name, absence.name) == 0 && strcmp(students[i].id, absence.id) == 0) {
            students[i].absences[students[i].num_absences] = absence;
            students[i].num_absences++;
            printf("Absence added.\n");
            return;
        }
    }
    // If the student wasn't found, create a new record for them
    Student student;
    strcpy(student.name, absence.name);
    strcpy(student.id, absence.id);
    student.absences[0] = absence;
    student.num_absences = 1;
    students[num_students] = student;
    num_students++;
    printf("Student and absence added.\n");
}

void modify_absence() {
    char name[50];
    char id[20];
    printf("Enter the name and ID of the student whose absence you want to modify:\n");
    scanf("%s %s", name, id);
    
    // Find the student
    int i, j;
    for (i = 0; i < num_students; i++) {
        if (strcmp(students[i].name, name) == 0 && strcmp(students[i].id, id) == 0) {
            // Display the student's absences and prompt the user to choose one to modify
            printf("Student found. Here are their absences:\n");
            for (j = 0; j < students[i].num_absences; j++) {
                printf("%d %d %s %s %s %s\n", students[i].absences[j].day, students[i].absences[j].period,
                    students[i].absences[j].course, students[i].absences[j].name, students[i].absences[j].id,
                    students[i].absences[j].type);
            }
            printf("Enter the number of the absence you want to modify:\n");
            int num;
            scanf("%d", &num);
            if (num < 0 || num >= students[i].num_absences) {
                printf("Invalid absence number.\n");
                return;
            }
            // Modify the absence
            Absence absence = students[i].absences[num];
            printf("Enter new information for the absence:\n");
            printf("Day: ");
            scanf("%d", &absence.day);
            printf("Period: ");
            scanf("%d", &absence.period);
            printf("Course: ");
            scanf("%s", absence.course);
            printf("Name: ");
            scanf("%s", absence.name);
            printf("ID: ");
            scanf("%s", absence.id);
            printf("Type (late, early, leave, absent): ");
            scanf("%s", absence.type);
            students[i].absences[num] = absence;
            printf("Absence modified.\n");
            return;
        }
    }
    printf("Student not found.\n");
}

void display_student() {
    char name[50];
    char id[20];
    printf("Enter the name and ID of the student whose absences you want to display:\n");
    scanf("%s %s", name, id);
    
    // Find the student and display their absences
    int i, j;
    for (i = 0; i < num_students; i++) {
        if (strcmp(students[i].name, name) == 0 && strcmp(students[i].id, id) == 0) {
            printf("Student found. Here are their absences:\n");
            for (j = 0; j < students[i].num_absences; j++) {
                printf("%d %d %s %s %s %s\n", students[i].absences[j].day, students[i].absences[j].period,
                    students[i].absences[j].course, students[i].absences[j].name, students[i].absences[j].id,
                    students[i].absences[j].type);
            }
            return;
        }
    }
    printf("Student not found.\n");
}

void sort_students(int arr[], int n) {
    int i, j;
    for (i = 0; i < n-1; i++) {
        for (j = 0; j < n-i-1; j++) {
            if (arr[j] < arr[j+1]) {
                int temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
}

void display_ranked_students() {
    int start_day, end_day;
    printf("Enter the starting and ending days of the period you want to check:\n");
    scanf("%d %d", &start_day, &end_day);
    
    // Count the number of absences for each student in the period
    int num_absences[num_students];
    int i, j;
    for (i = 0; i < num_students; i++) {
        num_absences[i] = 0;
        for (j = 0; j < students[i].num_absences; j++) {
            if (students[i].absences[j].day >= start_day && students[i].absences[j].day <= end_day
                && strcmp(students[i].absences[j].type, "absent") == 0) {
                num_absences[i]++;
            }
        }
    }
    
    // Sort the students by number of absences and display them
    sort_students(num_absences, num_students);
    printf("Students ranked by number of absences:\n");
    for (i = 0; i < num_students; i++) {
        for (j = 0; j < num_students; j++) {
            if (num_absences[i] == 0) {
                break;
            }
            if (strcmp(students[j].id, "") != 0 && num_absences[i] == students[j].num_absences) {
                printf("%s: %d absences\n", students[j].name, num_absences[i]);
                students[j].id[0] = '\0'; // Mark the student as already displayed
                break;
            }
        }
    }
}

void display_ranked_courses() {
    int start_day, end_day;
    printf("Enter the starting and ending days of the period you want to check:\n");
    scanf("%d %d", &start_day, &end_day);
    
    // Count the number of absences for each course in the period
    char courses[MAX_ABSENCES][50];
    int num_absences[MAX_ABSENCES];
    int num_courses = 0;
    int i, j, k;
    for (i = 0; i < num_students; i++) {
        for (j = 0; j < students[i].num_absences; j++) {
            if (students[i].absences[j].day >= start_day && students[i].absences[j].day <= end_day
                && strcmp(students[i].absences[j].type, "absent") == 0) {
                // Check if the course has already been added to the array
                int found = 0;
                for (k = 0; k < num_courses; k++) {
                    if (strcmp(courses[k], students[i].absences[j].course) == 0) {
                        num_absences[k]++;
                        found = 1;
                        break;
                    }
                }
                // If not, add it
                if (!found) {
                    strcpy(courses[num_courses], students[i].absences[j].course);
                    num_absences[num_courses] = 1;
                    num_courses++;
                }
            }
        }
    }
    
    // Sort the courses by number of absences and display them
    sort_students(num_absences, num_courses);
    printf("Courses ranked by number of absences:\n");
    for (i = 0; i < num_courses; i++) {
        for (j = 0; j < num_courses; j++) {
            if (num_absences[i] == 0) {
                break;
            }
            if (strcmp(courses[j], "") != 0 && num_absences[i] == num_absences[j]) {
                printf("%s: %d absences\n", courses[j], num_absences[i]);
                courses[j][0] = '\0'; // Mark the course as already displayed
                break;
            }
        }
    }
}

int main() {
    int choice;
    do {
        printf("\nAttendance System Main Menu\n");
        printf("1. Add an absence\n");
        printf("2. Modify an absence\n");
        printf("3. Display a student's absences\n");
        printf("4. Display ranked list of students with most absences\n");
        printf("5. Display ranked list of courses with most absences\n");
        printf("6. Quit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                add_absence();
                break;
            case 2:
                modify_absence();
                break;
            case 3:
                display_student();
                break;
            case 4:
                display_ranked_students();
                break;
            case 5:
                display_ranked_courses();
                break;
            case 6:
                printf("Goodbye!\n");
                break;
            default:
                printf("Invalid choice.\n");
                break;
        }
    } while (choice != 6);
    return 0;
}

该程序使用结构体来存储每个学生的考勤记录，并提供了菜单选项来添加、修改、查询和统计缺课记录。`sort_students`函数使用冒泡排序将一个整数数组按降序排列。`display_ranked_students`和`display_ranked_courses`函数分别统计某段时间内旷课最多的学生和课程，并按旷课次数由多到少排序后显示。