//genscore.c -- @CopyLeft by tsaiwn@csie.nctu.edu.tw
#define FILE_NAME "studat.txt"
#define ID_BASE 9917001
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
char nameLast[ ][3]={"趙", "錢", "孫", "李", "陳", "林", "陳", "林",
     "吳", "魏", "王", "蔡", "章", "張","簡", "馬","蘇" }; //陳林 2 倍機會
const int N_LAST = (sizeof nameLast / sizeof(nameLast[0]) );
#define NSTU_MIN  81357
#define NSTU_VAR 200
#define NSTU_MAX  (NSTU_MIN + NSTU_VAR)
int myRand( ) {
   int ans = rand( ) % 100;  // 不好, 因 uniform distribution// 0..99
   if(ans < 50) ans += 66;  // 太低就加 66 分
   return ans % 100;  // ensure 0..99, 若還變成很低就不管囉!
}
void genName(char*p) {
  char mm, m2, m3;  char tmps[8]={0};
  *p = 0;  // 清除字串; 其實是讓字串一開始就結束
  strcat(p, nameLast[rand( )% N_LAST]);
  mm = 'A' + rand( )%26;
  m2 = 'A' + rand( )%26;
  m3 = 'a' + rand( )%26;
  sprintf(tmps, "%c%c%c", mm, m2, m3);
  strcat(p, tmps);   // 把 tmps 串接到字串 p 尾巴  !
}    
extern int nStudent;
long genID( ) {
   static char idFlag[NSTU_MAX + 1];
   int k = rand( ) % nStudent;  // 一開始用亂數決定 
   int nTry = 0;
   while(idFlag[k] !=0) {
       k = rand( ) % nStudent;
       if(++nTry > 10) break;   // 試10次就放棄..
   }         //.. 然後改用由開始往後慢慢找沒有用過的
   if(idFlag[k]!=0) { //  k 已經用過
      k=0;
      while(idFlag[k] !=0) ++k;   // 逐一慢慢找沒有用過的
   }
   idFlag[k] = 1;   // 找到了, 就用 k, 並標示為用過了
   return ID_BASE + k;
}
///
 int nStudent;
 long sid;
 char name[9];
 int hwk, mid, quiz, fin;   // homework, midterm, quiz, final exam
void getNextStuData( ) {
   sid = genID( ); genName(name);
   hwk = myRand( );   mid = myRand( );  quiz = myRand( );  fin = myRand( );
}
int main( ) {
    FILE* fp;   // file pointer for Open a data file
    int i;   printf(" wait...");
    srand( time(0) );  // randomize so that looks like TRUE Random !
    int n = NSTU_MIN + rand( ) % NSTU_VAR;    // 每次 run 人數不同
    nStudent = n;
    fp = fopen(FILE_NAME, "wt");   // Open, for write, text
    if(fp==0){fprintf(stderr,"?open %s error...\n",FILE_NAME); return 1; }
    for(i = 1; i<= n; ++i) {
       getNextStuData( );
       fprintf(fp, "%7d %9s %3d %3d %3d %3d\n",
         sid, name, hwk, mid, quiz, fin);
    }fclose(fp);
    fprintf(stderr, "File %s generated successfully.\n", FILE_NAME);
    fprintf(stderr, "Total %d student records.\n", n);
    return 0;
}