C++ structure coding questions.

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


typedef struct U_Information
{  //Create structure 
char Name [10];
char RRN [15];
char ID [16];
char Password [16];
char Phone [16];
char Address [40];
char Email [20];

 } } UI;

character file_name[256]="User Data1.txt"; //Set file name 

#define MAX_USER_DATA  100 //

UI g_user_data[MAX_USER_DATA]; //
int g_user_count; //

voidReadUserData() //Read saved user information 
{ 
  int index = 0; 
  FILE *p_file = fopen(gfile_name, "r"); 
  if(p_file != NULL){ 
  fread(&g_user_count, sizeof(int), 1, p_file); //
  for(index = 0; index < g_user_count; index++){ 
      fread(g_user_data + index, sizeof(UI), 1, p_file); //
  } 
  fclose(p_file); 
  } 
} 

save voidSaveUserData() // save user information to file 
{ 
  int index = 0; 
  FILE *p_file = fopen(gfile_name, "w"); 
  if(p_file != NULL){ 
  fwrite(&g_user_count, sizeof(int), 1, p_file); //
  for(index = 0; index < g_user_count; index++){ 
      fwrite(g_user_data + index, sizeof(UI), 1, p_file); //
  } 
      fclose(p_file);} } 

void GetPassword (char farm_password[]) // Make it look like * when entering a password 
{ 
  int input = 0, index = 0; 
  while(input != 13){ 
  input = getch(); //
  if(input == 13) parm_password[index] = 0; //
  else { 
      printf("*"); 
      parm_password[index++] = input; //
  } 
  } 
  printf("\n"); 
} 

Create a member ID by entering voidUserRegister() //user information 
{ 
  printf ("To register as a member, enter the following information:\n\n"); 

  printf("1. Input Name: "); 
  gets(g_user_data[g_user_count].Name);
  printf("2. Input RRN: "); 
  gets(g_user_data[g_user_count].RRN);
  printf("3. Input ID: "); 
  gets(g_user_data[g_user_count].ID);
  printf("4. Input Password: "); 
  gets(g_user_data[g_user_count].Password);
  printf("5. Input Phone Number: "); 
  gets(g_user_data[g_user_count].Phone);
  printf("6. Input Address: "); 
  gets(g_user_data[g_user_count].Address);
  printf("7. Input Email: "); 
  gets(g_user_data[g_user_count].Email);       

  g_user_count++; //

  printf ("You are a member". Please log in again. \n\n"); 
} 


int main () // Basic mail (enter member ID, password) 
       //->Success message on success, re-enter password if incorrect 
      //-> If the ID is incorrect, ask if you want to register as a member if there is no OR - Enter member information at YES Enter again at NO 
{
 int index = 0, input = 0; 
  char id[16], password[16], success_login = 0; 

   ReadUserData(); //

  while(!success_login){ 
  printf("Input ID: "); 
  gets(id); 
  printf("Input Password: "); 
  GetPassword(password); 

  for(index = 0; index < g_user_count; index++){ //
      if(!strcmp(g_user_data[index].ID, id)){ //
          if(!strcmp(g_user_data[index].Password, password)){ //
              success_login = 1; //
              printf ("You have successfully logged in". \n\n"); 
          } else printf ("Make sure your password is entered correctly." \n\n"); 
          break; 
      } 
  } 

  if(index == g_user_count){ //
      printf("ID not registered". Would you like to register? ( y / n ): "); 
      input = getche(); 
      printf("\n\n"); 
      if(input == 'y' || input == 'Y') UserRegister(); //
      else printf ("Please re-enter".\n\n"); 
  } 
  } 

  SaveUserData(); //
}