Lua function not returning the values

Question

I'm trying to write a lua function in which I pass two rectangles coordinates and receive the values on polar coordinates. Somehow the code I wrote returns an error and I can't see where I went wrong. How do I fix it?

io.write("Enter first coord: ")
F = io.read()
io.write("Enter second coord: ")
S = io.read()

A = tonumber(F)
T = tonumber(S)

getPolar(A,T)

function getPolar(x,y)
    mag = math.sqrt(x^2+y^2)
    ang = math.atan(y/x)
    return print("Magnitude: " .. tostring(mag) .. " Angle: " .. tostring(ang))
end

The error I receive is the following:

Polar.lua:9: attempt to call a nil value (global 'getPolar') stack traceback: Polar.lua:9: in main chunk [C]: in ?

Piglet · Accepted Answer · 2019-12-11 12:35:34Z

2

Lua is interpreted line by line.

You're calling getPolar befor you define it.

Move to function call behind the function definition to fix that.

Please note that print does not return a value so you can omit the return in your function.

You should use local variables wherever you can. It would make sense to restrict the scope of mag and ang to your function body.

Use math.atan2 to calculate the angle as it will handle the quadrants correctly. See https://de.wikipedia.org/wiki/Arctan2

function getPolar(x,y)
    local mag = math.sqrt(x^2+y^2)
    local ang = math.atan2(x,y)
    return mag, ang
end

local mag, ang = getPolar(A,T)
print("Magnitude: " .. tostring(mag) .. " Angle: " .. tostring(ang))

edited Dec 11, 2019 at 12:35

answered Dec 11, 2019 at 12:27

Piglet

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1 Comment

Levy Over a year ago

Fantastic! Thank you very much.

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