4.编写程序，输入n个学生的学号和成绩（有1位小数），按成绩从高到低排序输出，n 小于50，学号小于10位。C语言

以下是一个简单的实现，使用结构体存储学生信息，使用冒泡排序按成绩从高到低排序：

#include <stdio.h>
#define MAX_N 50
#define MAX_ID_LEN 10

typedef struct {
    char id[MAX_ID_LEN];
    float score;
} Student;

void swap(Student *a, Student *b) {
    Student temp = *a;
    *a = *b;
    *b = temp;
}

void bubble_sort(Student students[], int n) {
    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - i - 1; j++) {
            if (students[j].score < students[j + 1].score) {
                swap(&students[j], &students[j + 1]);
            }
        }
    }
}

int main() {
    int n;
    printf("Enter the number of students: ");
    scanf("%d", &n);

    Student students[MAX_N];
    for (int i = 0; i < n; i++) {
        printf("Enter student %d's id and score: ", i + 1);
        scanf("%s %f", students[i].id, &students[i].score);
    }

    bubble_sort(students, n);

    printf("Sorted by score:\n");
    for (int i = 0; i < n; i++) {
        printf("%s %.1f\n", students[i].id, students[i].score);
    }

    return 0;
}

注意，此程序没有对输入的学号进行长度限制，如果需要可以在输入时进行判断。