c语言，功能简单的电话簿，实现输入，显示，查找的功能

感谢论坛里给我提供建议和意见的人，是你们的陪伴让我在风雨中前行，谢谢你们

特别感谢@NeilHappy ,@codesnail ,@xiakan008 ，你们对程序的完善提供的建设性的指导意见

c代码如下：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define LEN sizeof(struct mystr)
void main()
{
struct mystr
{
char name[40];
char add[100];
char code[20];
char tel[20];
struct mystr *next;
};
FILE *fp;
struct mystr *head,*p1,*p2;
char select,useless,search_name[40];
int out_err_flag=0,search_flag=0;

if((fp=fopen("phonebook.txt","ab+"))==NULL)
{printf("File open error!\n");exit(0);}

/*SELECT MENU*/

printf("1.Insert a new record\n2.Display existed records\n");
printf("3.Search a record\nELSE Quit\nPlease give your choice:");
scanf("%c%c",&select,&useless);
/*select is 1, insert a new record*/
if(select=='1')
{
printf("NOTE: Use # to finish input\n");
p1=p2=(struct mystr *)malloc(LEN);
head=p1;
head->next=NULL;
do
{
printf("Input the name:");
gets(p1->name);
if(strcmp(p1->name,"#")==0)    break;
printf("Input the address:");
gets(p1->add);
if(strcmp(p1->add,"#")==0)    break;
printf("Input the post code:");
gets(p1->code);
if(strcmp(p1->code,"#")==0)    break;
printf("Input the telphone number:");
gets(p1->tel);
if(strcmp(p1->tel,"#")==0)    break;

/*write to phonebook.txt*/
if(fwrite(p1,LEN,1,fp)==0)    out_err_flag=1;

p1=(struct mystr *)malloc(LEN);
p2->next=p1;
p2=p1;
}while(1);
printf("With a '#', you have ended the input\n");
if(out_err_flag==1)
printf("Errors ocure when writing to file!\n");

}

/*select is 2, display existed records*/
else if(select=='2')
{
printf("NAME\tADD\tCODE\tTEL\n");
p1=(struct mystr *)malloc(LEN);
while(!feof(fp))
{
if(fread(p1,LEN,1,fp))
printf("%s\t%s\t%s\t%s\n",p1->name,p1->add,p1->code,p1->tel);
}
free(p1);
}

/*select is 3, do research*/
else if(select=='3')
{
printf("Support search by name, please give a name:");
gets(search_name);
p1=(struct mystr *)malloc(LEN);
while(!feof(fp))
{
if(fread(p1,LEN,1,fp))
if(strcmp(p1->name,search_name)==0)
{
printf("NAME\tADD\tCODE\tTEL\n");
printf("%s\t%s\t%s\t%s\n",p1->name,p1->add,p1->code,p1->tel);
search_flag=1;
}
}
if(search_flag!=1)
printf("Nothing matched!\n");
free(p1);
}

/*if select is anything else, quit*/
else    exit(0);
fclose(fp);

getch();
}