为什么这个代码编译运行的结果会出现很多00

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
FILE *fp;
char a[10]="";
int c;
fp=fopen("wenjian.txt","w");
fprintf(fp,"123456789\n");
fprintf(fp,"dadcxcaczczc\n");
fprintf(fp,"3e2fdsczxcz\n");
fclose(fp);
fp=fopen("wenjian.txt","r+");
while(fgets(a,10,fp)!=NULL)
fputs(a,stdout);
rewind(fp);
while((c=getc(fp))!=EOF)
{
switch(c)
{
case '\n':
printf("\n");
default:
printf("%02X ",c);
}
}
fprintf(fp,"%s\n",a);
printf("fp=%ld\n", ftell(fp));
while(fgets(a,10,fp)!=NULL)
fputs(a,stdout);
rewind(fp);
while((c=getc(fp))!=EOF)
{
switch(c)
{
case '\n':
printf("\n");
default:
printf("%02X ",c);
}
}
fclose(fp);
getchar();
getchar();
return 0;
}