io.write("What is your name? ")
local name = io.read()

io.write("How old are you? ")
local age = io.read()

print("Doubled: " .. age * 2)
print("Is it 16? " .. tostring(age == 16))
print("Type: " .. type(age))

print("Doubled: " .. age * 2)

Doubled: 32

print("Doubled: " .. age * 2)

Doubled: 32

print("Is it 16? " .. tostring(age == 16))

Is it 16? false

print("Is it 16? " .. tostring(age == 16))

Is it 16? false

io.write("How old are you? ")
local age = io.read()

if age > 10 then
    print("Older than ten.")
end

io.write("How old are you? ")
local age = io.read()

if age > 10 then
    print("Older than ten.")
end

Error: main.lua:4: attempt to compare number with string

local age = tonumber(io.read())

local age = tonumber(io.read())

tonumber("twelve")

'F' → Fullscreen

Build

Task 1: Ask Two Questions

Copy template-console and rename the copy 1-04-greet. Replace main.lua with this:

1
io.write("What is your name? ")
2
local name = io.read()
3

4
io.write("What is your favorite color? ")
5
local color = io.read()
6

7
print("Nice to meet you " .. name .. ".")
8
print("I like " .. color .. " too.")

What is your name? Ada [Enter]
What is your favorite color? blue [Enter]
Nice to meet you Ada.
I like blue too.

Run it and answer both questions. Then change the questions and the sentences to your own, and add a third question.

Notice the space at the end of "What is your name? ". Take it out and your answer is typed with its nose against the question mark.

Task 2: Three Kinds of Wrong

Copy the template again to 1-04-age, and write this:

1
io.write("How old are you? ")
2
local age = io.read()
3

4
print("Doubled: " .. age * 2)
5
print("Is it 16? " .. tostring(age == 16))
6
print("Type: " .. type(age))

Run it and type 16:

How old are you? 16 [Enter]
Doubled: 32
Is it 16? false
Type: string

Copy all three results onto your sheet. One worked, one was false, and one told you the type was string — even though you typed a number.

Now replace those three lines with a comparison:

1
io.write("How old are you? ")
2
local age = io.read()
3

4
if age > 10 then
5
    print("Older than ten.")
6
end

How old are you? 16 [Enter]

Error: main.lua:4: attempt to compare number with string

  main.lua:4: in main chunk

Copy that message onto your sheet too. Three different outcomes, one typed value.

Task 3: Fix It With One Word

Put the three print lines back, and change one line:

1
io.write("How old are you? ")
2
local age = tonumber(io.read())
3

4
print("Doubled: " .. age * 2)
5
print("Is it 16? " .. tostring(age == 16))
6
print("Type: " .. type(age))

How old are you? 16 [Enter]
Doubled: 32
Is it 16? true
Type: number

Put the comparison back as well and check that it no longer crashes.

Task 4: Use It for Something

Copy the template to 1-04-nextyear and write a program that asks for an age and answers with next year's:

1
io.write("How old are you? ")
2
local age = tonumber(io.read())
3

4
print("Next year you will be " .. age + 1 .. ".")

How old are you? 16 [Enter]
Next year you will be 17.

Then add a second question of your own that does arithmetic on the answer — a number of pets, a jersey number, a locker number. Anything you can add to or multiply.

Challenge (Optional): Break It on Purpose

Run 1-04-nextyear again and type twelve instead of a number:

How old are you? twelve [Enter]

Error: main.lua:4: attempt to perform arithmetic on local 'age' (a nil value)

  main.lua:4: in main chunk

tonumber did not crash. It handed back nil, and line 4 is where somebody finally tried to use it. Write down which line has the mistake and which line reported it.

This is the second time nil has turned up somewhere other than where it was made. It will keep doing that.

Checkpoint

• 1-04-greet asks three questions in your own wording and answers in sentences
• All three wrong results from task 2 are written on your sheet
• 1-04-age now reports number and true
• 1-04-nextyear does arithmetic on two typed answers

Reflection

Answer the following questions before submitting your work.

1. Of the three wrong results in task 2, say which one you think is the most dangerous in a real program, and why. The answer is not the one that crashed.
2. age * 2 gave 32 without tonumber. Explain why that is a problem rather than a convenience.
3. You typed a word at a number question and the program crashed on a line that looked fine. Describe how you would find the real cause if nobody had told you what you typed.

Submit

Submit the required files to the appropriate dropbox.

Activity Complete