用C语言编写对应权限登陆和重新登陆或退出

/*登陆*/
void log_in()
{
FILE *fp = NULL;
char user_name[21] = {0};
char password[21] = {0};
int is_default_pass = -1;
char in_user[21] = {0};
char in_pass[21] = {0};
char ch;

fp = fopen("code", "rb");
if(fp)
{
fscanf(fp, "%s\n%s", user_name, password);

if(strcmp("admin", user_name) == 0
&&strcmp("123456", password) == 0)
{
is_default_pass = 1;
}
else
{
is_default_pass = -1;
}
}

if(!fp || is_default_pass == 1)
{
if(!fp)
{
strcpy(user_name, "admin");
strcpy(password, "123456");
fp = fopen("code", "wb");
fprintf(fp, "%s\n%s", user_name, password);
fclose(fp);
fp = fopen("code", "rb");
}