优化下面的代码：#include <stdio.h>#include <stdlib.h>#include <string.h>typedef struct{ int id; int chinese; int math; int english; float average;}Student;int cmp(const void* a, const void* b){ Student* s1 = (Student*)a; Student* s2 = (Student*)b; if(s1->average != s2->average){ return s2->average - s1->average; }else{ return s1->id - s2->id; }}int main(){ int n; scanf("%d", &n); Student students[n]; memset(students, 0, sizeof(students)); for(int i = 0; i < n; i++){ scanf("%d %d %d %d", &students[i].id, &students[i].chinese, &students[i].math, &students[i].english); students[i].average = (float)(students[i].chinese + students[i].math + students[i].english) / 3; } qsort(students, n, sizeof(Student), cmp); for(int i = 0; i < n; i++){ printf("%d %d %d %d\n", students[i].id, students[i].chinese, students[i].math, students[i].english); } return 0;}

以下是优化后的代码：

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

typedef struct{
    int id;
    int chinese;
    int math;
    int english;
    float average;
}Student;

int cmp(const void* a, const void* b){
    Student* s1 = (Student*)a;
    Student* s2 = (Student*)b;
    if(s1->average != s2->average){
        return s2->average > s1->average ? 1 : -1;
    }else{
        return s1->id - s2->id;
    }
}

int main(){
    int n;
    scanf("%d", &n);
    Student *students = (Student*)malloc(n * sizeof(Student));
    for(int i = 0; i < n; i++){
        scanf("%d %d %d %d", &students[i].id, &students[i].chinese, &students[i].math, &students[i].english);
        students[i].average = (float)(students[i].chinese + students[i].math + students[i].english) / 3;
    }
    qsort(students, n, sizeof(Student), cmp);
    for(int i = 0; i < n; i++){
        printf("%d %d %d %d\n", students[i].id, students[i].chinese, students[i].math, students[i].english);
    }
    free(students);
    return 0;
}

该程序对原程序进行了如下优化：

1. 在结构体定义中去掉了头文件`string.h`的引用，因为该头文件并未被使用到。

2. 在比较函数`cmp`中，将`s2->average - s1->average`的判断改为了`s2->average > s1->average ? 1 : -1`的形式，因为前者可能会出现溢出的问题，而后者则可以避免这种情况的发生。

3. 在主函数中，使用了动态分配内存的方式来申请学生结构体数组，这样可以避免在编译时需要定义数组大小的问题。

4. 在程序结尾处，使用了`free`函数来释放动态分配的内存，避免内存泄漏的问题。