自定义结构体加手写快排，请dalao挑错

#include<iostream>

using namespace std;

struct Student{
	int ID,C,M,E,A;
};

void quicksort(Student a[],int l,int r){
	
	if(l >= r) return;
	int x = a[(l + r)/2].A;
	int i = l - 1,j = r + 1;
	while(i < j){
		do i++;while(a[i].A > x);
		do j--;while(a[j].A < x);
		if(i < j) swap(a[i],a[j]);
	}
	quicksort(a,l,j);
	quicksort(a,j+1,r);
	
}

int main(){
	
	int n;
	cin >> n;
	Student a[n + 1];
	for(int i = 1;i <= n;i++){
		cin >> a[i].C >> a[i].M >> a[i].E;
		a[i].A = a[i].C + a[i].M + a[i].E;
		a[i].ID = i;
	}
	quicksort(a,1,n);
	for(int i = 1;i <= 5;i++){
		cout << a[i].ID << " " << a[i].A << endl;
	}
	
	return 0;
}

来自三个月的蒟蒻的求助