Fitrst numbers in ListBox C++ Builder

private: // User declarations

        bool __fastcall is_First(int x);

        int *tab;

        int *difference_value;

        int *value_plus_one;

        void __fastcall init_Tab();

        void __fastcall destroyed_Tab();

#include <vcl.h>

#pragma hdrstop

#include "m_first01.h"

//---------------------------------------------------------------------------

#pragma package(smart_init)

#pragma resource "*.dfm"

#define max 5000

TForm1 *Form1;

//---------------------------------------------------------------------------

__fastcall TForm1::TForm1(TComponent* Owner)

        : TForm(Owner)

{

}

//---------------------------------------------------------------------------

bool __fastcall TForm1::is_First(int x)

{

 int i,sum;

 sum=0;

 for(i=1;i<x+1;i++)

  if(x%i==0)

   ++sum;

 if(sum==2)

  return true;

 else

  return false;

}

void __fastcall TForm1::init_Tab()

{

 tab=new int[max];

 difference_value=new int[max-1];

 value_plus_one=new int[max-1];

}

void __fastcall TForm1::destroyed_Tab()

{

 delete difference_value;

 delete value_plus_one;

 delete tab;

}

void __fastcall TForm1::Button1Click(TObject *Sender)

{

 destroyed_Tab();

 Close();

}

//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)

{

 init_Tab();

 int i,j;

 i=0;j=0;

 do

 {

  if(is_First(j))

  {

   tab[i]=j;

   ++i;

  }

  ++j;

 }while(i<max);

 for(i=-1,j=i+1;i<max-1;i++,j++)

 {

  difference_value[i+1]=tab[j+1]-tab[i+1];

  value_plus_one[i+1]=difference_value[i+1]+1;

 }

}

//---------------------------------------------------------------------------

void __fastcall TForm1::Button2Click(TObject *Sender)

{

 int i;

 ListBox1->Items->Clear();

 for(i=0;i<max;i++)

 {

  ListBox1->Items->Add(IntToStr(i+1)+")   "+IntToStr(tab[i]));

 }

 ListBox2->Items->Add("--------");

 for(i=0;i<max-1;i++)

 {

  ListBox2->Items->Add(IntToStr(i+1)+")   "+IntToStr(tab[i])+"   -   "+IntToStr(difference_value[i])+"   -   "+IntToStr(value_plus_one[i]));

 }

}

//---------------------------------------------------------------------------

void __fastcall TForm1::Button3Click(TObject *Sender)

{

 int i;

 ListBox3->Items->Clear();

 i=0;

 do

 {

   if((!is_First(difference_value[i])) && (!is_First(value_plus_one[i])))

   {

    ListBox3->Items->Add(IntToStr(tab[i])+"  -  "+IntToStr(difference_value[i])+"  - "+IntToStr(value_plus_one[i]));

   }

   ++i;

 }while(i<max-1);

}

//---------------------------------------------------------------------------

void __fastcall TForm1::Button4Click(TObject *Sender)

{

 int i;

 ListBox4->Items->Clear();

 i=0;

 do

 {

   if((is_First(difference_value[i])) && (is_First(value_plus_one[i])))

   {

    ListBox4->Items->Add(IntToStr(tab[i])+"  -  "+IntToStr(difference_value[i])+"  - "+IntToStr(value_plus_one[i]));

   }

   ++i;

 }while(i<max-1);

}

//---------------------------------------------------------------------------