用c语言定义一个结构体数组，存放10个学生的学号，姓名，三门课的成绩 2．从键盘输入10个学生的以上内容 3．输出单门课成绩最高的学生的学号、姓名、以及该门课程的成绩 4．输出三门课程的平均分数最高的学生的学号、姓名及其平均分 5．将10个学生按照平均分数从高到低进行排序，输出结果，

以下是实现该功能的C语言代码：

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

#define NUM_STUDENTS 10
#define NUM_COURSES 3

struct student {
    int id;
    char name[20];
    int scores[NUM_COURSES];
    float avg_score;
};

void input_students(struct student students[]);
void print_highest_score(struct student students[]);
void print_highest_avg(struct student students[]);
void sort_students(struct student students[]);

int main() {
    struct student students[NUM_STUDENTS];
    input_students(students);
    print_highest_score(students);
    print_highest_avg(students);
    sort_students(students);
    printf("\nRanking of students by average score:\n");
    for (int i = 0; i < NUM_STUDENTS; i++) {
        printf("%d. %s (ID: %d) - Average Score: %.2f\n", i+1, students[i].name, students[i].id, students[i].avg_score);
    }
    return 0;
}

void input_students(struct student students[]) {
    for (int i = 0; i < NUM_STUDENTS; i++) {
        printf("Enter information for student %d:\n", i+1);
        printf("ID: ");
        scanf("%d", &students[i].id);
        printf("Name: ");
        scanf("%s", students[i].name);
        for (int j = 0; j < NUM_COURSES; j++) {
            printf("Score for course %d: ", j+1);
            scanf("%d", &students[i].scores[j]);
        }
        float sum_scores = 0;
        for (int j = 0; j < NUM_COURSES; j++) {
            sum_scores += students[i].scores[j];
        }
        students[i].avg_score = sum_scores / NUM_COURSES;
    }
}

void print_highest_score(struct student students[]) {
    int highest_score = 0;
    struct student highest_scoring_student;
    for (int i = 0; i < NUM_STUDENTS; i++) {
        for (int j = 0; j < NUM_COURSES; j++) {
            if (students[i].scores[j] > highest_score) {
                highest_score = students[i].scores[j];
                highest_scoring_student = students[i];
            }
        }
    }
    printf("\nStudent with highest score:\n");
    printf("Name: %s (ID: %d)\n", highest_scoring_student.name, highest_scoring_student.id);
    printf("Highest Score: %d\n", highest_score);
}

void print_highest_avg(struct student students[]) {
    float highest_avg = 0;
    struct student highest_avg_student;
    for (int i = 0; i < NUM_STUDENTS; i++) {
        if (students[i].avg_score > highest_avg) {
            highest_avg = students[i].avg_score;
            highest_avg_student = students[i];
        }
    }
    printf("\nStudent with highest average score:\n");
    printf("Name: %s (ID: %d)\n", highest_avg_student.name, highest_avg_student.id);
    printf("Average Score: %.2f\n", highest_avg);
}

void sort_students(struct student students[]) {
    struct student temp;
    for (int i = 0; i < NUM_STUDENTS; i++) {
        for (int j = i+1; j < NUM_STUDENTS; j++) {
            if (students[j].avg_score > students[i].avg_score) {
                temp = students[i];
                students[i] = students[j];
                students[j] = temp;
            }
        }
    }
}

该程序定义了一个结构体 `student`，包括学号、姓名、三门课的成绩和平均分数。通过 `input_students()` 函数从键盘输入学生信息，计算平均分数。然后，通过 `print_highest_score()` 函数输出单门课成绩最高的学生信息，通过 `print_highest_avg()` 函数输出三门课程的平均分数最高的学生信息，最后通过 `sort_students()` 函数将学生按照平均分数从高到低进行排序，并输出排名结果。