C语言 注册系统登录

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

int length_password(char *p)
{
 int len;
 len = strlen(p);
 if(len<6||len>12)
 {
  return 0;
 }
 else
  return len;
}

int password_valid(char *p)
{
 int i=0;

 for(;*p != '\0'; p++)
 {
  if(!( (*p >= 'a' && *p <= 'z') || (*p >= 'A' && *p <='Z') 
   ||(*p >='0' && *p <= '9')))
   return 0;
 }
 return 1;
}


int Regester()