StringGrid, заполняется только квадратная составляющая

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
 
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma link "CSPIN"
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
RichEdit1 -> Clear();
RichEdit2 -> Clear();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
 
n = StrToInt (RichEdit1 -> Text);
m = StrToInt (RichEdit2 -> Text);
A = n;
B = m;
StringGrid1 -> ColCount = m+1;
StringGrid1 -> RowCount = n+1;
StringGrid2 -> ColCount = m+1;
StringGrid2 -> RowCount = n+1;
StringGrid3 -> ColCount = m+1;
StringGrid3 -> RowCount = n+1;
 
for(i = 1; i <= n; i++)
{
for(j = 1; j <= m; j++)
{
StringGrid1->Cells[0][i]=IntToStr(i);
StringGrid1->Cells[i][0]=IntToStr(i);
StringGrid2->Cells[0][i]=IntToStr(i);
StringGrid2->Cells[i][0]=IntToStr(i);
StringGrid3->Cells[0][i]=IntToStr(i);
StringGrid3->Cells[i][0]=IntToStr(i);
}
}
for(i = 1; i < (n + 1); i++)
{
for(j = 1; j < (m + 1); j++)
{
StringGrid1 -> Cells[i][j] = IntToStr(random(21)-10);
StringGrid2 -> Cells[i][j] = IntToStr(random(21)-10);
}
}
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Button2Click(TObject *Sender)
{
for (i = 1; i <= (A); i++)
{
for (j = 1; j <= (B); j++)
{
a = StrToInt(StringGrid1->Cells[i][j]);
b = StrToInt(StringGrid2->Cells[i][j]);
StringGrid3 -> Cells[i][j] = IntToStr(a - b);
}
}
 
}
//---------------------------------------------------------------------------
 
 
void __fastcall TForm1::Button3Click(TObject *Sender)
{
RichEdit1 -> Clear();
RichEdit2 -> Clear();
for (i = 1; i <= (A); i++)
{
for (j = 1; j <= (B); j++)
{
StringGrid1 -> Cells[i][j] = " ";
StringGrid2 -> Cells[i][j] = " ";
StringGrid3 -> Cells[i][j] = " ";
}
}
 
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button4Click(TObject *Sender)
{
  Close();
}
//---------------------------------------------------------------------------

     TStringList *sl = new TStringList ;
     for (int i=0;i<StringGrid3->RowCount;i++)
       sl->Add(StringGrid3->Rows[i]->CommaText);
     sl->SaveToFile("File.txt");
     delete sl;