Resoudre une equation du second degres

if !variable_local_exists('create')
{
a = get_integer('a = ',0)
b = get_integer('b = ',0)
c = get_integer('c = ',0)

D = b*b - 4*a*c

if (D > 0)
{
    x1 = (-b+sqrt(D))/(2*a)
    x2 = (-b-sqrt(D))/(2*a)
}
else
if (D == 0)
{
    x_ = -b/(2*a)
}
else
if (D < 0)
{
    x1r = -b/(2*a)
    x1i = -sqrt(-D)/(2*a)
    x2r = -b/(2*a)
    x2i = sqrt(-D)*(2*a)
}
create = 0
}

if !keyboard_check(vk_space)
{
draw_text(8 ,8 + 16*0 ,"a = "+string(a) )
draw_text(8 ,8 + 16*1 ,"b = "+string(b) )
draw_text(8 ,8 + 16*2 ,"c = "+string(c) )

draw_text(8 ,8 + 16*4 ,"D = "+string(D) )

if D>0
{
    draw_text(8 ,8 + 16*6 ,"x1 = "+string(x1) )
    draw_text(8 ,8 + 16*7 ,"x2 = "+string(x2) )
}
else
if D==0
draw_text(8 ,8 + 16*6 ,"x = "+string(x_) )
else
if D<0
{
    draw_text(8 ,8 + 16*6 ,"x1 = "+string(x1r)+" + "+string(x1i)+"i" )
    draw_text(8 ,8 + 16*7 ,"x2 = "+string(x2r)+" + "+string(x2i)+"i" )
}
}

if !keyboard_check(vk_space) exit

draw_line(0,240,640,240)
draw_line(320,0,320,480)

for(i=-16 ; i<=16 ; i+=0.05)
{
    j = i+0.05
    draw_line(i*20 +320, -(a*i*i + b*i + c) + 240 , j*20 +320 , -(a*j*j + b*j + c) + 240 )
    draw_line(i*20*10*2,240-4,i*20*10*2,240+4)
    draw_line(i*20*10,240-2,i*20*10,240+2)
}