How do I allow a person to buy this from a GUI/shop?

I tried to do this it didn't work so I believe that I did something wrong. (Yes its a local script.)

local stock = game.Players.LocalPlayer:WaitForChild("Stocks").ONE.Value
local cash = game.Players.LocalPlayer:WaitForChild("leaderstats").Cash.Value
local OPrice = game.Workspace.ONEVal.ONEPrice
local a = game.StarterGui.CashNStuff.Frame.Investments.Buy1
 
local stock = tonumber(a.Text)
a.Text = tostring(stock)
script.Parent.MouseButton1Click:connect(function()
  if cash > OPrice.Value then 
	stock = stock + 1 and cash == cash - OPrice.value and a.Text == tostring(stock)
	else print("Not enough cash")
end
end)

UPDATED still error

You can't compare an integer value to a string value which you do:

if cash == game.Workspace.Board.SurfaceGui.SmoothGUI.PriceONE.Text 

The cash is an integer (number), while the text is a string value. Possibly using an IntValue object and comparing cash to that, I would suggest using a > sign rather than = would work. Hope this helped!

Johner to fix your error that you commented under JackOfAllBlox's answer, you would use tostring() and tonumber(). This converts the stringvalue of the number to a number, and you could change it back to the string after performing the arithmetic. For example,

local a = game.StarterGui.ScreenGui.Frame.TextLabel.Text

local b = tonumber(a)
b = b + 1
a = tostring(b)

Edit: Actually that script would not work since I did TextLabel.Text I would have to do:

local a = game.StarterGui.ScreenGui.Frame.TextLabel

local b = tonumber(a.Text)
b = b + 1
a.Text = tostring(b)