sin/cos grapher

--Terminal size
local w,h = term.getSize()
if w < 50 then w = w-5
else w = 50 end
if h < 20 then h = h-4
else h = 20 end

--Query function
local function ask(q,c)
    if not c then c = colors.white end
    term.clear()
    term.setCursorPos(1,1)
    term.setTextColour(c)
    term.write(q)
    term.setTextColour(colors.white)
    term.setCursorPos(1,2)
    return read()
end

--Parameter capture
term.clear()

local type = ask("Type of wave? (sin/cos)")
while type ~= "sin" and type ~= "cos" do
    type = ask("Type of wave? (sin/cos)")
end
local p = {}
p.a = tonumber(ask("Value for 'a'?"))
while not p.a do
    p.a = tonumber(ask("Value for 'a'? (Please enter a number value.)"))
end
p.b = ask("Value for 'b'?")
while not p.a do
    p.b = tonumber(ask("Value for 'b'? (Please enter a number value.)"))
end
p.c = ask("Value for 'c'?")
while not p.a do
    p.c = tonumber(ask("Value for 'c'? (Please enter a number value.)"))
end
p.d = ask("Value for 'd'?")
while not p.a do
    p.d = tonumber(ask("Value for 'd'? (Please enter a number value.)"))
end
local anim = ask("Animated? (y/n)")
while anim ~= "y" and anim ~= "n" do
    anim = ask("Animated? (y/n)")
end

--Pixel plotting function
local function ppix(x,y,b,c,t)
    --x/y = position of pixel
    --c = color
    --t = text
    term.setCursorPos(x,y)
    term.setTextColour(c)
    term.setBackgroundColor(b)
    term.write(t)
    term.setTextColour(colors.white)
    term.setBackgroundColor(colors.black)
end

local function txt(y,t)
    term.setTextColor(colors.white)
    term.setBackgroundColor(colors.black)
    term.setCursorPos(1,y)
    term.write(t)
end

--draws border and parameters for graph
local function drawFrame(p)
    --top/bottom
    for i=2, w-1 do
        ppix(i,1,colors.black,colors.yellow,"_")
        ppix(i,h,colors.black,colors.yellow,"_")
    end
    --sides
    for i=2, h do
        ppix(1,i,colors.black,colors.yellow,"|")
        ppix(w,i,colors.black,colors.yellow,"|")
    end
    txt(h+2,"y = "..type.."("..p.b.."x".."+"..p.c..")+"..p.d)
    txt(h+3,"Amplitude: "..(p.a))
    txt(h+4,"Period: 2pi/"..p.b)
    txt(h+5,"Displacement: "..(-p.c/p.b))
    txt(h+6,"Vertical Displacement: "..p.d)
end

--p = parameter table, i = x value increment. defaults to 0 in the drawWave function
local function calcSin(p,x,i)
    return p.a*math.sin(p.b*(x+i)+p.c)+p.d
end

local function calcCos(p,x,i)
    return p.a*math.cos(p.b*(x+i)+p.c)+p.d
end

local calc = calcSin

--Single frame graph function
local function drawWave(p,i)
    if not i then i = 0 end
    for x = 2, w-1 do
        local y = calc(p,x-2,i)
        if y < h-1 and y+5 > 1 then
            ppix(x,y+5,colors.black,colors.red,".")
        end
    end
    drawFrame(p) --ERROR: Trying to grab variable 'type' before it gets assigned
end

--Animation function
local function animWave(p,speed)
    for i = 0, 1000, speed do
        term.clear()
        drawWave(p,i)
        ppix(w-24,h+2,colors.black,colors.white,"X animation increment: "..speed)
        os.sleep(0.2)
    end
end

--Function assignment
if type == "cos" then
    calc = calcCos
end

--Program execution
if anim == "y" then
    local speed = tonumber(ask("Animation speed?"))
    while not speed do
        speed = tonumber(ask("Animation speed? (enter a number value to increment X by)"))
    end
    animWave(p,speed)
elseif anim == "n" then
    drawWave(p)
end

--Done statement
ppix(1,30,colors.white,colors.blue,"...Done!")