程序代码：

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

#define AMOUNT 50000000

int main()
{
FILE * fpnum=fopen("numout.txt","w+");
FILE * fpstr=fopen("strout.txt","w+");
int num=0;
char ch;
int i;
for(i=0;i<AMOUNT;i++)
{
  if(!(i%1000))
    srand((unsigned)time(NULL));//每产生1000个后，重设随机数种子
  num=rand()%8;
  fprintf(fpnum,"%d",num);
  switch(num/2)
  {
         case 0:
             ch='A';
             break;
         case 1:
             ch='B';
             break;
         case 2:
             ch='C';
             break;
         case 3:
             ch='D';
             break;
  }
  fputc(ch,fpstr);
    }
fclose(fpnum);
fclose(fpstr);
return 0;
}