setscreen ("graphics:max,max")
View.Set ("title:Parabola Grapher")
var c, y, d, a, b : real
var username : string := Sys.GetUserName
a := -51
b := 0
c := 0
d := 1
put "Welcome ",username,","
put ""
put "The equation of a parabola is as follows:"
put "y=ax**2+b"
put ""
put "Enter a value for a."
get d
put "Enter a value for b."
get c
cls
for i : 3 .. maxx by 10
    drawline (i, 0, i, maxx, grey)
end for
for j : 0 .. maxy by 10
    drawline (0, j, maxx, j, grey)
end for
drawline (maxx div 2, 0, maxx div 2, maxy, black)
drawline (0, maxy div 2, maxx, maxy div 2, black)
for x : -maxx .. maxx
    y := d * x ** 2 + c
    a := x - 1
    b := x - 1 ** 2
    drawline (round (a + maxx div 2), round (d * a ** 2 + c + maxy div 2), round (x + maxx div 2), round (y + maxy div 2), black)
    drawfilloval (round (x + maxx div 2), round (y + maxy div 2), 2, 2, red)
end for