I want to zoom a flag i made in c graphics. I have made a try using setaspectratio function but its not working. What is wrong with program. How can i zoom in the flag by just pressing '+' operator?

#include<graphics.h>
#include<stdio.h>
#include<conio.h>
int main()
{
int gdriver=VGA, gmode=VGAHI;
int x1=100,y1=120,x2=300,y2=240,i,xasp,yasp;
float midx,midy;
char ch;

initgraph(&gdriver, &gmode,"C:\\TURBOC3\\BGI");
getaspectratio(&xasp, &yasp);
do
{
if(ch=='+')
setaspectratio(xasp+=100,yasp+=100);

rectangle(x1,y1,x2,y2);
line(x1,y1+40,x2,y1+40);
line(x1,y1+80,x2,y1+80);

bar(x1-5,y1,x1-2,y1+280);

midx= (x2+x1)/2;
midy= (y2+y1)/2;
setrgbpalette(23,21,15,10);

setfillstyle(SOLID_FILL,22);
floodfill(x1+1,y1+1,getmaxx());

setfillstyle(SOLID_FILL,WHITE);
floodfill(x1+1,y1+41,getmaxx());

setfillstyle(SOLID_FILL,GREEN);
floodfill(x1+1,y1+81,getmaxx());

setfillstyle(SOLID_FILL,BLUE);

for(i=0; i<=345; i+=15)
{
sector(midx,midy,i,i+15,20,20);
}
getchar();
cleardevice();
}while(ch=='+');

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