RT，感谢神犇相助。

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <unordered_map>
#include <vector>

using namespace std;

const int N = 110;
const double eps = 1e-5; // avoid EOF

int idx; // student number
struct Student {
    string sid; // Student ID
    int cid; // Class ID
    string name; // Begin with a capital letter
    int score[8]; // Chinese, Math, English, Programming
    bool is_exist;
} s[N], tmp[N];

int get_total(Student a) { // Calculate Student's total score
    int total = 0;
    for (int i = 1; i <= 4; ++i) total += a.score[i];
    return total;
}

void msort(Student s[], int l, int r) { // Sort the Students
    if (l >= r) return ;

    int mid = l + r >> 1;
    msort(s, l, mid), msort(s, mid+1, r);

    int i = l, j = mid+1, k = 1;
    while (i <= mid && j <= r) {
        if (get_total(s[i]) >= get_total(s[j])) tmp[k ++] = s[i ++];
        else tmp[k ++] = s[j ++];
    }

    while (i <= mid) tmp[k ++] = s[i ++];
    while (j <= r) tmp[k ++] = s[j ++];

    for (int i = l, j = 1; i <= r; ++i, ++j) s[i] = tmp[j];
}

void Main_Menu() { // Operations 
    puts("Welcome to Student Performance Management System (SPMS).");
    puts("");
    puts("1 - Add");
    puts("2 - Remove");
    puts("3 - Query");
    puts("4 - Show ranking");
    puts("5 - Show Statistics");   
    puts("0 - Exit");
    puts("");
}

void Add() { // Add student(s) (operation 1)
    idx ++;
    puts("Please enter the SID, CID, name and four scores. Enter 0 to finish.");
    cin >> s[idx].sid;
    while (s[idx].sid != "0") {
        cin >> s[idx].cid >> s[idx].name;
        for (int i = 1; i <= 4; ++i) cin >> s[idx].score[i];
        s[idx].is_exist = 1;
     
        // If the sid has appeared
        bool flag = 0;
        for (int i = 1; i < idx; ++i) {
            if (s[i].sid == s[idx].sid) {
                flag = 1;
                break;
            }
        }
        if (flag) {
            idx --; // Ignore the duplicated SID.
            puts("Duplicated SID.");
        }

        idx ++;
        printf("Please enter the SID, CID, name and four scores. ");
        puts("Enter 0 to finish.");
        cin >> s[idx].sid;
    }

    idx --;
}

void Remove() { // Remove student(s) (operation 2)
    string ss;
    puts("Please enter SID or name. Enter 0 to finish.");
    cin >> ss;
    while (ss != "0") {
    	int cnt = 0;
        if (isdigit(ss[0])) { // User inputs a sid
            // If the sid is in the queue
            for (int i = 1; i <= idx; ++i) {
                if (s[i].sid == ss && s[i].is_exist) {
                    s[i].is_exist = 0;
                    cnt ++;
                }
            }
        } else { // User inputs a name
            for (int i = 1; i <= idx; ++i) {
                if (s[i].name == ss && s[i].is_exist) {
                    s[i].is_exist = 0;
                    cnt ++;
                }
            }
        }
		
		printf("%d student(s) removed.\n", cnt);
		puts("Please enter SID or name. Enter 0 to finish.");
        cin >> ss;
    }
}

void Query() { // Query student's rank (operation 3)
    string ss;
    puts("Please enter SID or name. Enter 0 to finish.");
    cin >> ss;

    msort(s, 1, idx);
    while (ss != "0") {
        int cnt = 0;
        if (isdigit(ss[0])) {
            for (int i = 1; i <= idx; ++i) {
                if (s[i].is_exist) cnt ++;
                if (s[i].sid == ss && s[i].is_exist) {
                    cout << cnt << " " << s[i].sid << " " << s[i].cid << " ";
                    cout << s[i].name << " ";
                    for (int j = 1; j <= 4; ++j) printf ("%d ", s[i].score[j]);
                    printf("%d %.2f\n", get_total(s[i]), get_total(s[i])/4.0+eps);
                } 
            }
        } else {
            for (int i = 1; i <= idx; ++i) {
                if (s[i].is_exist) cnt ++;
                if (s[i].name == ss && s[i].is_exist) {
                    cout << cnt << " " << s[i].sid << " " << s[i].cid << " ";
                    cout << s[i].name << " ";
                    for (int j = 1; j <= 4; ++j) printf ("%d ", s[i].score[j]);
                    printf("%d %.2f\n", get_total(s[i]), get_total(s[i])/4.0+eps);
                } 
            }
        }

        puts("Please enter SID or name. Enter 0 to finish.");
        cin >> ss;
    }
}

void Show_Ranklist() { // Show the Ranklist :) (operation 4)
    puts("Showing the ranklist hurts students\' self-esteem. Don\'t do that.");
}

void Show_Statistics() { // Show students' score (operation 5) 
    puts("Please enter class ID, 0 for the whole statistics.");
    int cid;
    cin >> cid;

    int sum[8] = {}, pass[8] = {}, fail[8] = {};
    int pass_total[8] = {};
    int num = 0; // number of students 
    if (cid == 0) { // Counting ...
        for (int i = 1; i <= idx; ++i) {
            if (s[i].is_exist) {
                int cnt = 0;
                for (int j = 1; j <= 4; ++j) {
                    sum[j] += s[i].score[j];
                    if (s[i].score[j] >= 60) pass[j] ++, cnt ++;
                    else fail[j] ++;
                }
                pass_total[cnt] ++;
                num ++;
            }
        }
    } else {
        for (int i = 1; i <= idx; ++i) {
            if (s[i].cid == cid && s[i].is_exist) {
                int cnt = 0;
                for (int j = 1; j <= 4; ++j) {
                    sum[j] += s[i].score[j];
                    if (s[i].score[j] >= 60) pass[j] ++, cnt ++;
                    else fail[j] ++;
                }
                pass_total[cnt] ++;
                num ++;
            }
        }
    }

    for (int i = 1; i <= 4; ++i) {
        // Subjects
        if (i == 1) puts("Chinese");
        else if (i == 2) puts("Mathematics");
        else if (i == 3) puts("English");
        else puts("Programming");

        printf("Average Score: %.2f\n", (double)(sum[i])/num);
        printf("Number of passed students: %d\n", pass[i]);
        printf("Number of failed students: %d\n", fail[i]);
        puts("");
    }

    puts("Overall:");
    printf("Number of students who passed all subjects: %d\n", pass_total[4]);
    printf("Number of students who passed 3 or more subjects: %d\n", pass_total[3]+pass_total[4]);
    printf("Number of students who passed 2 or more subjects: %d\n", pass_total[2]+pass_total[3]+pass_total[4]);
    printf("Number of students who passed 1 or more subjects: %d\n", pass_total[1]+pass_total[2]+pass_total[3]+pass_total[4]);
    printf("Number of students who failed all subjects: %d\n", pass_total[0]);
    puts("");
}

int main() {
//	freopen("UVA12412.out", "w", stdout);
	
    Main_Menu();
    int op;
    while (1) {
        cin >> op;
        if (op == 0) break;
        else if (op == 1) Add();
        else if (op == 2) Remove();
        else if (op == 3) Query();
        else if (op == 4) Show_Ranklist();
        else Show_Statistics();

        Main_Menu();
    }
//    system("pause");
    return 0;
}