題解：

一個大一的C語言大作業。（只是缺少了文件輸入輸出orzz）

主要思想就是一個一個功能實現，從簡單的做起，比如0和4.

但是做了一天都debug找不出哪裡錯了，可以說不熟悉stl導致各種bug。以後做還是用陣列的方法避免隱藏得很厲害的bug。

這個ac不了下面貼出佳哥的程式碼。比我短多了而且還過了。

#include<stdio.h>
#include<string.h>
#define maxn 1000
#define maxl 100
#define EPS 1e-5
 
int n = 0;
char sid[maxn][maxl];
int cid[maxn];
char name[maxn][maxl];
int score[maxn][5];
int removed[maxn];
 
const char* course_name[] = {"Chinese", "Mathematics", "English", "Programming"};
 
int valid (int k)
{
    for (int i = 0; i < k; i++) if (!removed[i])
        {
            if (strcmp (sid[i], sid[k]) == 0) return 0;
        }
    return 1;
}
 
void add()
{
    for (;;)
    {
        printf ("Please enter the SID, CID, name and four scores. Enter 0 to finish.\n");
        scanf ("%s", sid[n]);
        if (strcmp (sid[n], "0") == 0) break;
        scanf ("%d%s%d%d%d%d", &cid[n], name[n], &score[n][0], &score[n][1], &score[n][2], &score[n][3]);
        if (valid (n))
        {
            score[n][4] = score[n][0] + score[n][1] + score[n][2] + score[n][3];
            n++;
        }
        else printf ("Duplicated SID.\n");
    }
}
 
int rank (int k)
{
    int r = 0;
    for (int i = 0; i < n; i++)
        if (!removed[i] && score[i][4] > score[k][4]) r++;
    return r + 1;
}
 
void DQ (int isq)
{
    char s[maxl];
    for (;;)
    {
        printf ("Please enter SID or name. Enter 0 to finish.\n");
        scanf ("%s", s);
        if (strcmp (s, "0") == 0) break;
        int r = 0;
        for (int i = 0; i < n; i++) if (!removed[i])
            {
                if (strcmp (sid[i], s) == 0 || strcmp (name[i], s) == 0)
                {
                    if (isq) printf ("%d %s %d %s %d %d %d %d %d %.2f\n", rank (i), sid[i], cid[i], name[i], score[i][0], score[i][1], score[i][2], score[i][3], score[i][4], score[i][4] / 4.0 + EPS);
                    else
                    {
                        removed[i] = 1;
                        r++;
                    }
                }
            }
        if (!isq) printf ("%d student(s) removed.\n", r);
    }
}
 
double get_course_stat (int c, int s, int* passed, int* failed)
{
    int tot = 0;
    *passed = *failed = 0;
    for (int i = 0; i < n; i++)
        if (!removed[i] && (c == 0 || cid[i] == c))
        {
            tot += score[i][s];
            if (score[i][s] >= 60) (*passed)++;
            else (*failed)++;
        }
    return (double) tot / (double) (*passed + *failed);
}
 
void get_overall_stat (int c, int* cnt)
{
    cnt[0] = cnt[1] = cnt[2] = cnt[3] = cnt[4] = 0;
    for (int i = 0; i < n; i++)
        if (!removed[i] && (c == 0 || cid[i] == c))
        {
            int k = 0;
            for (int j = 0; j < 4; j++) if (score[i][j] >= 60) k++;
            cnt[k]++;
        }
}
 
void stat()
{
    int c;
    printf ("Please enter class ID, 0 for the whole statistics.\n");
    scanf ("%d", &c);
    for (int i = 0; i < 4; i++)
    {
        int passed, failed;
        double avg = get_course_stat (c, i, &passed, &failed);
        printf ("%s\n", course_name[i]);
        printf ("Average Score: %.2f\n", avg + EPS);
        printf ("Number of passed students: %d\n", passed);
        printf ("Number of failed students: %d\n", failed);
        printf ("\n");
    }
    int cnt[5];
    get_overall_stat (c, cnt);
    printf ("Overall:\n");
    printf ("Number of students who passed all subjects: %d\n", cnt[4]);
    printf ("Number of students who passed 3 or more subjects: %d\n", cnt[4] + cnt[3]);
    printf ("Number of students who passed 2 or more subjects: %d\n", cnt[4] + cnt[3] + cnt[2]);
    printf ("Number of students who passed 1 or more subjects: %d\n", cnt[4] + cnt[3] + cnt[2] + cnt[1]);
    printf ("Number of students who failed all subjects: %d\n", cnt[0]);
    printf ("\n");
}
 
int main()
{
	//freopen("in.txt","r",stdin);
	//freopen("out.txt","w",stdout);
    for (;;)
    {
        int choice;
        printf ("Welcome to Student Performance Management System (SPMS).\n");
        printf ("\n");
        printf ("1 - Add\n");
        printf ("2 - Remove\n");
        printf ("3 - Query\n");
        printf ("4 - Show ranking\n");
        printf ("5 - Show Statistics\n");
        printf ("0 - Exit\n");
        printf ("\n");
        scanf ("%d", &choice);
        if (choice == 0) break;
        if (choice == 1) add();
        if (choice == 2) DQ (0);
        if (choice == 3) DQ (1);
        if (choice == 4) printf ("Showing the ranklist hurts students' self-esteem. Don't do that.\n");
        if (choice == 5) stat();
    }
    return 0;
}