C++ fstream Edit File/Database

/* fstream Edit File/Database By Moses Limbo
*/
#include <conio.h>
#include <stdio.h>
#include <iostream.h>
#include <string.h>
#include <stdlib.h>
#include <fstream.h>

struct{
 char user[20],pass[20],name[50],address[50],course[20],section[20];
}mehh[50];

char input[50];
int ctr=0,opt=0,len=0,flag=0,eopt=0;

void load(),save(),space(),unspace(),login(),reg(),view(),edit(),loginmenu(),modify();

void main(){
 clrscr();
 load();
 cout<<"[1] Login\n[2] Register\n[3] Exit\n";
 cin>>opt;
 switch (opt){
  case 1: login(); break;
  case 2: reg(); break;
  default: exit(0);
 }
}

void login(){
 char luser[20],lpass[20];
 clrscr();
 cout<<"Username: ";
 cin>>luser;
 cout<<"Password: ";
 cin>>lpass;
 for (int m=0;m<ctr;m++){
  if(!strcmp(luser,mehh[m].user)&&!strcmp(lpass,mehh[m].pass)){
   loginmenu();
   flag=1;
  }
 }
 if(flag==0){
  cout<<"Incorrect Username or Password...";
  getch();
  main();
 }
}

void reg(){
 clrscr();
 cout<<"Username: ";
 cin>>mehh[ctr].user;
 cout<<"Password: ";
 cin>>mehh[ctr].pass;
 cout<<"Name: ";
 unspace();
 strcpy(mehh[ctr].name,input);
 cout<<"Address: ";
 unspace();
 strcpy(mehh[ctr].address,input);
 cout<<"Course: ";
 cin>>mehh[ctr].course;
 cout<<"Section: ";
 cin>>mehh[ctr].section;
 cout<<"Login Successful";
 getch();
 ctr++;
 save();
 main();
}

void loginmenu(){
 clrscr();
 cout<<"[1] View\n[2] Edit\n[3] Logout";
 cin>>opt;
 switch(opt){
  case 1: view(); break;
  case 2: edit(); break;
  case 3: main(); break;
  default: main();
 }
}

void view(){
 clrscr();
 for(int n=0; n<ctr; n++){
  cout<<"Id: "<<n+1<<endl<<endl;
  cout<<"Username: "<<mehh[n].user<<endl;
  cout<<"Password: "<<mehh[n].pass<<endl;
  cout<<"Name: ";
  strcpy(input,mehh[n].name);
  space();
  cout<<"Address: ";
  strcpy(input,mehh[n].address);
  space();
  cout<<"Course: "<<mehh[n].course<<endl;
  cout<<"Section: "<<mehh[n].section<<endl;
  cout<<endl;
 }
 getch();
 loginmenu();
}

void edit(){
 clrscr();
 for(int i=0;i<ctr;i++){
  cout<<i+1<<"\t"<<mehh[i].user<<endl;
 }
 cout<<"Enter ID: ";
 cin>>eopt;
 eopt-=1;
 clrscr();
 cout<<"Edit: ";
 cout<<"1. Username\n2. Password\n3. Name\n4. Address\n5. Course\n6. Section\n";
 cin>>opt;
 switch(opt){
  case 1: cout<<"Username: ";
      gets(mehh[eopt].user);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  case 2: cout<<"Password: ";
      gets(mehh[eopt].pass);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  case 3: cout<<"Name: "; unspace();
      strcpy(mehh[eopt].name,input);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  case 4: cout<<"Address: "; unspace();
      strcpy(mehh[eopt].address,input);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  case 5: cout<<"course: ";
      gets(mehh[eopt].course);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  case 6: cout<<"section: ";
      gets(mehh[eopt].section);
      cout<<"Edit successful...";
      getch();
      modify(); //modifies the file
      main(); break;
  default: main();
 }
}

void load(){
  ifstream read;
  read.open("mehh.txt");
  read>>ctr;
  for (int i=0;i<ctr;i++){
   read>>mehh[i].user>>mehh[i].pass>>mehh[i].name>>mehh[i].address>>mehh[i].course>>mehh[i].section;
  }
  read.close();
}

void save(){
 ofstream write;
 write.open("mehh.txt");
 write<<ctr<<endl;
 for (int j=0;j<ctr;j++){
 write<<mehh[j].user<<" "<<mehh[j].pass<<" "<<mehh[j].name<<" "<<mehh[j].address<<" "<<mehh[j].course<<" "<<mehh[j].section<<endl;
 }
 write.close();
}

void modify(){ //function to edit the file
 ofstream write;
 write.open("mehh.txt");
 write<<ctr<<endl;
 for (int j=0;j<ctr;j++){
 if(j==eopt){ //to match what id to replace and overwrite the certain line...
  write<<mehh[eopt].user<<" "<<mehh[eopt].pass<<" "<<mehh[eopt].name<<" "<<mehh[eopt].address<<" "<<mehh[eopt].course<<" "<<mehh[eopt].section<<endl;
  }
 else{ //if it doesn't match
   write<<mehh[j].user<<" "<<mehh[j].pass<<" "<<mehh[j].name<<" "<<mehh[j].address<<" "<<mehh[j].course<<" "<<mehh[j].section<<endl;
  }
 }
 write.close();
}

void unspace(){
 gets(input);
 len=strlen(input);
 for (int k=0;k<len;k++){
  if (input[k]==' '){
   input[k]='_';
  }
 }
}

void space(){
 len=strlen(input);
 for (int l=0;l<len;l++){
  if (input[l]=='_'){
   input[l]=' ';
  }
 }
 cout<<input<<endl;
}