Графика в С++ 3.1

[N@t@ly1992]

Программа считает значение функции и потом рисует ее график...
Проблема в том, что график рисует неправильно

#include<iostream.h>
#include<math.h>
#include<conio.h>
#include<stdio.h>
#include<graphics.h>
#include<stdlib.h>

int main()

{
{
double x,y,k,a,b,c,s=-1;
int xn,xk,h;
cout<<"a=";cin>>a;
cout<<"b=";cin>>b;
cout<<"c=";cin>>c;
cout<<"xn=";cin>>xn;
cout<<"xk=";cin>>xk;
cout<<"h=";cin>>h;
for (int i=xn;i<xk;i+=h)
{if((i+c<0)&(a!=0))y=(a*i*i*i-b)*s;
else if((i+c>0)&(a==0))y=(i-a)/(i-c);
else y=i/c+c/i;
printf("\n %d %g\n",i,y);

}
int l,Y,N;
cout<<"Graphik: Y-yes,N-no ";
cin>>l;
if(l==Y);
{
int gdriver = DETECT, gmode, errorcode;
int Xmax, Ymax;


initgraph(&gdriver, &gmode, "D:\\BORLANDC\\BGI");
errorcode = graphresult();

if (errorcode != grOk)
{
printf("Graphics error: %s\n", grapherrormsg(errorcode));
printf("Press any key to halt:");
getch();
exit(1);
}

float y0=240;
float x0=320;
float h=20;
line(x0,h,x0,480-h);
line(x0,h,x0+5,h+15);
line(x0,h,x0-5,h+15);
line(h,y0,640-h,y0);
line(640-h,y0,640-h-15,y0+5);
line(640-h,y0,640-h-15,y0-5);

for (int i=10; i<600; i+20)
{
i=i+20;
line(i,245,i,235);
}

int k;
for (k=20; k<480; k+20)
{
k=k+20;
line(310,k,330,k);
}
char s[4]=" ";

for ( int n=20; n<=600; n+20)
{ for (int t=-14; t<=15; t++)

{outtextxy(n, 250, gcvt(t,5,s));
n=n+20;
}

{char m[4]=" ";

for ( int l=40; l<=100; l+25)
{ for (int k=10; k>=1; k--)

{outtextxy(335, l, gcvt(k,6,m));
l=l+20; }
{char m2[4]=" ";

for ( int l2=260; l2<=480; l2+25)
{ for (int k2=-1; k2>=-11; k2--)

{outtextxy(337, l2, gcvt(k2,6,m2));
l2=l2+20; }
moveto(x0,y0);

int px,py,s=-1;
float dx=0.0001;

if((i+c<0)&(a!=0))y=(a*i*i*i-b)*s;
else if((i+c>0)&(a==0))y=(i-a)/(i-c);
else y=i/c+c/i;
px=300+i*200;
py=240-y*200;
setcolor(RED);

x+=dx;
lineto(px,py);



getch();
closegraph;
return 0;
}
}}}}}}}