Creating a text editor in c++ without using any graphics library [the function is undeclared error]

I am creating a texteditor in c++[non gui] , So far i have ended up with this code.. i get two undeclared errors... Why?

#include <iostream>
#include <fstream>

using namespace std;


int main()
{
    int op;
    cout<<"do you want to open example.txt or overwrite?\nIf you want to overwrite enter 1 , if you want to view it enter开发者_如何转开发 2. :\n";
    cin>>op;
    if(op==1)
    {
        edit();
    }
    else if(op==2)
    {
        open();
    }
}

void edit()
{
    int op;
    string x;
    ofstream a_file("example.txt" , ios::app);
    cout<<"HEY ENTER SOME TEXT TO BE WRITTEN TO EXAMPLE.txt [created by rohan bojja]\n--------------------------------------------------------------------------------\n";
    getline ( cin , x);
    a_file<<x;
    cout<<"want to type in an other line?\n1 for YES, 2 for NO";
    cin>>op;
   while(op==1)
   {
       a_file<<"\n";
       edit;
   }
   cout<<"Do you want to quit?\n1 for YES , 2 for NO";
    cin>>op;
    if (op==2)
    {
    edit;
    }
}
void open()
{
    int op;
    ifstream a_file("example.txt");
    cout<<"You are now viewing example.txt [created by rohan bojja]\n--------------------------------------------------------------------------------\n";
    cout<<a_file;
    cout<<"Do you want to quit?\n1 for YES , 2 for NO";
    cin>>op;
   if(op==2)
    {
        open;
    }
}

but , while compiling i get the error [CodeBlocks Build Log]:

F:\Projects\c++\TextEditor\texteditor.cpp: In function 'int main()':
F:\Projects\c++\TextEditor\texteditor.cpp:14: error: 'edit' was not declared in this scope
F:\Projects\c++\TextEditor\texteditor.cpp:18: error: 'open' was not declared in this scope

---

Your main function can't see the edit and open functions because they appears after main. You can fix this by either:

1) Moving the edit and open functions above main; or

2) Adding a prototype of edit and open above main. Add this line of code before main, but after using namespace std:

void edit();
void open();

---

C++ compiler is a one pass compiler. Which means it reads from top to bottom and translates your code. If you are using a function (or any other symbol), the compiler should know about it before it reaches it.

Now you have two options, either put main under edit and open, or write a so-called forward declaration:

void edit();
void open();

That is basically the function you have without its body. Note that this kind of things are what is put in .h files (headers) when you have multiple source files.

---

You need to declare symbols (functions, variables, etc.) before you use them. To fix your problem, forward declare your functions.

#include <...>
using namespace std;

void edit();
void open();

int main ()
{
    // ...
}

void open ()
{
    // ...
}

void edit ()
{
    // ...
}