【正确答案】①#include"stdio.h"
   main()
   {
   FILE*fp;
   char ch,fname[20];
   printf("please input file name:\n");
   scanf("/%s",fname);
   if((fp=fopen(fname,"w"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   printf("please input some text:\n");
   ch=getchar();
   while((ch=getchar())!='＄')
   fputc(ch,fp);
   fclose(fp);
   printf("\nthe content ofthe file/%s is:\n",fname);
   if((fp=fopen(fname,"r"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   while(!feof(fp))
   {
   ch=fgetc(fp);
   putchar(ch);
   }
   fclose(fp);
   }
   ②#include"stdio.h"
   main()
   {
   struct person{
   char name[20];
   char sex;
   int age;
   float height;
   }personl;
   FILE*fp;
   char fname[20];
   int i;
   printf("please input a file name:\n");
   scanf("/%s",fname);
   if((fp=fopen(fname,"wb"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   printf("please input thlee persons'name,sex,age and height:\n");
   for(i=0;i＜3;i++)
   {
   scant("/%s/%c/%d/%f",person1.name,＆person1.sex,＆person1.age,＆person1.height);
   if(fwrite(＆person1,sizeof(person1),1,fp)!=1)
   {
   prinff("write error!\n");
   exit(0);
   }
   fclose(fp);
   if((fp=fopen(fname,"lb"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   printf("\nthe content ofthe file is:\nName\t\tSex\tAge\tHeight\n");
   while(!feof(fp))
   {
   if(fread(＆person1,sizeof(personl),1,fp)==1)
   printf("/%-16s/%-8c/%-8d/%-10.2f\n",person1.name,person1.sex,person1.age,person 1.height);
   }
   fclose(fp);
   }
   ③#include"stdio.h"
   main()
   {
   struc t person
   {char name[20];
   char sex:
   int age;
   float height;
   }person1;
   FILE*fp;
   char fname[20];
   int i;
   printf("please input a file name:\n");
   scanf("/%s",fname);
   if((fp=fopen(fname,"wb"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   printf("please input three persons'name,sex,age and height:\n");
   for(i=0;i＜3;i++)
   {
   scanf("/%s  /%c/%d/%f",person1.name,  ＆person1.sex,  ＆person1.age,＆person 1.height);
   if(fwrite(＆person1,sizeof(personl),1,fD)!=1)
   {
   printf("write error!\n");
   exit(0);
   }
   }
   fclose(fp);
   if((fp=fopen(fname,"rb"))==NULL)
   {
   printf("cannot open this file!\n");
   exit(0);
   }
   printf("please input the sequence number(0、1 or 2):\n");
   scanf("/%d",＆i);
   printf("\nthe information about this person is:\nName\t\tSex\lAge\tHeight\n");
   fseek(fp,i*sizeof(person1),0);
   if(fread(＆person1,sizeof(person1),1,fp)==1)
   printf("/%-16s/%-8c/%-8d/%-10.2f\n",person1.name,person1.sex,person1.age,person 1．height);
   fclose(fp);
   }