Return a usable price

v3 · Activity 5 of 12 · return-values · early-return · 9 min Runs here

Chapter outline

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One step at a time

print exposes a value to a person; return gives it to the caller. A function without a returned value supplies nil.

return also stops the current function call. A guard at the top can reject a bad input before the main calculation.

Your task

price(quantity, unitPrice) returns 0 for a negative quantity; otherwise it returns quantity * unitPrice. The caller needs the number, not only Output. Keep the final return shown in the starter so the checker can call or inspect your result.

Interface: price(quantity, unitPrice) -> number

Input	Expected
Normal purchase`3, 6`	`18`
Empty purchase`0, 6`	`0`
Invalid count`-1, 6`	`0`

See another example

local function points(count)
    if count < 0 then return 0 end
    return count * 5
end
local total = points(3) + 2
print(total)
return points

points returns 15, allowing the caller to add 2. Merely printing 15 would not supply that value to +.

Syntax in this activity

New syntax: early return, negative numbers

Earlier ideas used here

functions
parameters
return-values
comparison
if-else

Explain more

print exposes a value to a person; return gives it to the caller. A function without a returned value supplies nil.

return also stops the current function call. A guard at the top can reject a bad input before the main calculation.

Our rule treats a negative quantity as invalid and returns 0. This is an exercise policy, not a complete store security design.

Explain this code

Select a word or symbol in this authored example. Your editor draft stays unchanged.

  pricequantity, unitPrice
     quantity  0 
        0
    
    quantity  unitPrice

 price

Choose a highlighted part to see what it means.

Free experiment

This is a private experiment copy. It does not replace your answer or complete the activity.

These inputs apply when your scratchpad returns the function described by the activity interface.

Test different inputs

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local function points(count)
    if count < 0 then return 0 end
    return count * 5
end
local total = points(3) + 2
print(total)
return points

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Experiment Output

Your output will appear here.

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Code

Luau

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local function price(quantity, unitPrice)
    if quantity < 0 then
        print(0)
    end
    print(quantity * unitPrice)
end
return price

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Your output will appear here.

Ready

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Your task

Interface: price(quantity, unitPrice) -> number

Input	Expected
Normal purchase`3, 6`	`18`
Empty purchase`0, 6`	`0`
Invalid count`-1, 6`	`0`

See another example

local function points(count)
    if count < 0 then return 0 end
    return count * 5
end
local total = points(3) + 2
print(total)
return points

points returns 15, allowing the caller to add 2. Merely printing 15 would not supply that value to +.

Syntax in this activity

New syntax: early return, negative numbers

Earlier ideas used here

functions
parameters
return-values
comparison
if-else

Explain more

print exposes a value to a person; return gives it to the caller. A function without a returned value supplies nil.

return also stops the current function call. A guard at the top can reject a bad input before the main calculation.

Our rule treats a negative quantity as invalid and returns 0. This is an exercise policy, not a complete store security design.

Explain this code

Select a word or symbol in this authored example. Your editor draft stays unchanged.

  pricequantity, unitPrice
     quantity  0 
        0
    
    quantity  unitPrice

 price

Choose a highlighted part to see what it means.

Free experiment

This is a private experiment copy. It does not replace your answer or complete the activity.

These inputs apply when your scratchpad returns the function described by the activity interface.

Test different inputs

Font size Plain text

local function points(count)
    if count < 0 then return 0 end
    return count * 5
end
local total = points(3) + 2
print(total)
return points

Luau keyword highlighting · Ctrl/⌘ + Enter: Run · Esc: leave editorTab inserts indentation

Experiment Output

Your output will appear here.