Выдает ошибку типо деление на 0 хотя на 0 ни где у меня не делится

//---------------------------------------------------------------------------
 
#include <vcl.h>
#include<math.h>
#include<iostream.h>
#include <stdio.h>
#pragma hdrstop
 
#include "Unit1.h"
#include "Unit2.h"
#include "Unit3.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma link "CSPIN"
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
}
//---------------------------------------------------------------------------
 
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
 
StringGrid1->Cells[0][0] = "N";
StringGrid1->Cells[1][0] = "Xi";
StringGrid1->Cells[2][0] = "Yi";
 
 
 
StringGrid2->Cells[0][0] = "Ñóììà Xi";
StringGrid2->Cells[1][0] = "Ñóììà Yi";
StringGrid2->Cells[2][0] = "Ñóììà Xi^2";
StringGrid2->Cells[3][0] = "Ñóììà Yi^2";
StringGrid2->Cells[4][0] = "Ñóììà Yi*Xi";
StringGrid2->Cells[5][0] = "Êîðåëÿöèÿ r";
 
}
//---------------------------------------------------------------------------//---------------------------------------------------------------------------}
//---------------------------------------------------------------------------
 
 
 
 
void __fastcall TForm1::CSpinEdit1Change(TObject *Sender)
{
     StringGrid1->RowCount=CSpinEdit1->Value+2;
     float m;
     m=CSpinEdit1->Value;
     for (int i=1; i<=m; i++)
       StringGrid1->Cells[0][i]=IntToStr(i);
     StringGrid1->Cells[0][m+1]="";
}
//---------------------------------------------------------------------------
 
 
 
void __fastcall TForm1::N5Click(TObject *Sender)
{
Form1->Close();
}
//---------------------------------------------------------------------------
 
 
 
 
void __fastcall TForm1::Button4Click(TObject *Sender)
{
    for(int i = 0; i < StringGrid1->ColCount; i++)
    for(int j = 0; j < StringGrid1->RowCount; j++)
    StringGrid1->Cells[i+1][j+1] = "";
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::Button1Click(TObject *Sender)
{
int I,J;
double x,y,r;
float x2,y2,z,c,d,c2,c3,t1,t2,c1,c4;
DecimalSeparator = '.';//aeiaaeuiay aioo?aiiyy ia?aiaiiay
J=StringGrid1->RowCount-2;
for(I=1; I<=J ; I++)
{
x+=StrToFloat(StringGrid1->Cells[1][I]);
y+=StrToFloat(StringGrid1->Cells[2][I]);
x2+=pow((StrToFloat(StringGrid1->Cells[1][I])),2);
y2+=pow((StrToFloat(StringGrid1->Cells[2][I])),2);
z+=(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));
d=StrToFloat(StringGrid1->Cells[0][I]);
c=d*z-x*y;
t1=d*x2;
t2=pow(x,2);
c1=t1-t2;
c2=(d*y2)-(pow(y,2));
c3=(c1)*(c2);
c4=sqrt(c3);
r=c/c4;
 
}
StringGrid2->Cells[0][StringGrid2->RowCount-1] = FloatToStr(x);
StringGrid2->Cells[1][StringGrid2->RowCount-1] = FloatToStr(y);
StringGrid2->Cells[2][StringGrid2->RowCount-1] = FloatToStr(x2);
StringGrid2->Cells[3][StringGrid2->RowCount-1] = FloatToStr(y2);
StringGrid2->Cells[4][StringGrid2->RowCount-1] = FloatToStr(z);
StringGrid2->Cells[5][StringGrid2->RowCount-1] = FloatToStr(z);
 
}
//---------------------------------------------------------------------------
 
 
void __fastcall TForm1::Button2Click(TObject *Sender)
{
float r;
r=StrToFloat(StringGrid2->Cells[5][1]);
if (r>0)
 {
 Form2->ShowModal();
 }
if (r<0)
 {
 Form3->ShowModal();
 }
 if (r=0)
  {
  ShowMessage ("Êîððåëÿöèÿ ðàâíà 0 (Åñëè ñ èçìåíåíèåì x çíà÷åíèÿ Y â ñðåäíåì íå èçìåíÿþòñÿ, òî ãîâîðÿò, ÷òî êîððåëÿöèÿ – íóëåâàÿ.)");
 }
}
//---------------------------------------------------------------------------

r=c/c4;

z+=(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));

z+=(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));

z=z+(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));

z+=(StrToFloat(StringGrid1->Cells[1][I]))*(StrToFloat(StringGrid1->Cells[2][I]));