CODEWITHSUNDEEP
stringlualua-patterns
user3314993
user3314993

Reputation: 287

Error when take two numbers out of a string

I'm just playing around with Lua trying to make a calculator that uses string manipulation. Basically I take two numbers out of a string, then do something to them (+ - * /). I can successfully take a number out of x, but taking a number out of y always returns nil. Can anyone help?

local x = "5 * 75"

function calculate(s)
    local x, y =
    tonumber(s:sub(1, string.find(s," ")-1)),
    tonumber(s:sub(string.find(s," ")+3), string.len(s))
    return x * y
end

print(calculate(x))

Upvotes: 2

Views: 57

Answers (1)

MartinValen
MartinValen

Reputation: 93

You have a simple misplaced parenthesis, sending string.len to tonumber instead of sub.

local x, y =
tonumber(s:sub(1, string.find(s," ")-1)),
tonumber(s:sub(string.find(s," ")+3, string.len(s)))

You actually don't need the string.len, as end of string is the default value for sub if nothing is given.

EDIT: You can actually do what you want to do way shorter by using string.match instead.

local x,y = string.match(s,"(%d+).-(%d+)")

Match looks for tries to match the string with the pattern given and returns the captured values, in this case the numbers. This pattern translates to "One or more digits, then as few as possible of any character, then one or more digits". %d is 1 digit, + means one or more. . means any character and - means as few as possible. The values within the parentheses are captured, which means that they are returned.

Upvotes: 3

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