程序代码：

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>


typedef struct info info;
    struct info
    {
        int age;
        char name[20];
        char cellphone[12];
        char qqid[12];
        info *next;
    };


void get_name (info *current)
{
    printf ("请输入联系人姓名：");
    fgets (current->name,20,stdin);
    int len=strnlen_s (current->name,sizeof (current->name));
    if (current->name[len-1]=='\n')
    {
        current->name[len-1]='\0';
    }
}


void get_qqid (info *current)
{
    printf ("请输入当前联系人的QQ号码：");
    fgets (current->qqid,12,stdin);
    int len=strnlen_s (current->qqid,sizeof (current->qqid));
    if (current->qqid[len-1]=='\n')
    {
        current->qqid[len-1]='\0';
    }
}


void write_file (FILE *pfile,char *filename,info *first,info *current,info *previous)
{
    current=first;

    while (current!=NULL)
    {
        if (fopen_s (&pfile,filename,"wb+"))
        {
            printf ("打开文件失败");
            exit (1);
        }

        int len=strnlen_s (current->name,sizeof (current->name));
        fprintf (pfile,"%4d",len);
        fwrite (current->name,sizeof (char),len,pfile);
        fwrite (current->cellphone,sizeof (char),11,pfile);
        len=strnlen_s (current->qqid,sizeof (current->qqid));
        fprintf (pfile,"%-4d",len);
        fwrite (current->qqid,sizeof (char),len,pfile);
        fprintf (pfile,"%4d",current->age);
        previous=current;
        current=current->next;
        free (previous);
        previous=NULL;
    }
    first=NULL;
    fclose (pfile);
}


void get_person (info *current)
{
    get_name (current);
    fflush (stdin);
    putchar (10);
    printf ("请输入当前联系人的年龄：");
    scanf_s ("%d",&current->age,sizeof (int));
    fflush (stdin);
    putchar (10);
    printf ("请输入当前联系人的手机号：");
    fgets (current->cellphone,12,stdin);
    fflush (stdin);
    putchar (10);
    get_qqid (current);
    fflush (stdin);
}


bool find_info (FILE *pfile,char *filename)
{
    int len;
    int flen;
    bool find=false;
    info temp;
    char temp_name[20];
    char cell[12]={'\0'};
    char qq[12]={'\0'};
    if(fopen_s (&pfile,filename,"rb+"))
    {
        printf ("打开文件失败。");
        exit (1);
    }

    printf ("请输入要修改联系人的姓名：");
    fflush (stdin);
    fgets (temp_name,20,stdin);
    
    while (1)
    {
        fscanf (pfile,"%4d",&len);
        fread (temp_name,sizeof (char),len,pfile);
        fread (cell,sizeof (char),11,pfile);
        fscanf (pfile,"%d",&flen);
        fread (qq,sizeof (char),flen,pfile);
        fscanf (pfile,"%4d",&temp.age);
        if (strcmp (temp_name,temp.name)==0)
        {
            printf ("联系人已经找到.");
            find =true;
            break;
        }
        if (feof (pfile))
        {
            break;
        }
    }
    return find;
}

int main ()
{
    info *first=NULL;
    info *current=NULL;
    info *previous=NULL;
    char buf[100];
    char answer='\0';
    bool find=false;
    FILE *pfile=NULL;
    char *filename="info.bin";

        
     for ( ; ; )
     {
         if (first==NULL)
         {
             printf ("请输入第一个联系人的信息：");
             putchar (10);
         }
         else
         {
             printf ("是否继续输入? y or n :");
             scanf_s ("%c",&answer,sizeof (char));
             fflush (stdin);
             if (tolower (answer)=='n')
             {
                 break;
             }
         }

         current=(info*)malloc (sizeof (info));
         if (first==NULL)
         {
             first=current;
         }
         
         if (previous!=NULL)
         {
             previous->next=current;
         }

         get_person (current);
         current->next=NULL;
         previous=current;
    }
    write_file (pfile,filename,first,current,previous);
    find=find_info (pfile,filename);
      system ("pause");
    return 0;
}