print(10 + 3)
print(10 - 3)
print(10 * 3)
print(10 / 3)
print(10 % 3)
print(2 ^ 3)

print(10 + 3)
print(10 - 3)
print(10 * 3)
print(10 / 3)
print(10 % 3)
print(2 ^ 3)

13
7
30
3.3333333333333
1
8

print(10 / 2)
print(10 / 4)
print(17 / 5)

print(10 / 2)
print(10 / 4)
print(17 / 5)

5
2.5
3.4

print(10 / 4)
print(math.floor(10 / 4))

2.5
2

print(2 + 3 * 4)
print((2 + 3) * 4)

print(2 + 3 * 4)
print((2 + 3) * 4)

14
20

local a = 80
local b = 90
local c = 100

print("Average: " .. a + b + c / 3)

local a = 80
local b = 90
local c = 100

print("Average: " .. a + b + c / 3)

Average: 203.33333333333

print("Average: " .. (a + b + c) / 3)

Average: 90

print("Average: " .. (a + b + c) / 3)

Average: 90

'F' → Fullscreen

Build

Task 1: Run the Six

Copy template-console to 1-05-math and write this:

1
print(10 + 3)
2
print(10 - 3)
3
print(10 * 3)
4
print(10 / 3)
5
print(10 % 3)
6
print(2 ^ 3)

13
7
30
3.3333333333333
1
8

Copy all six answers onto your sheet. Then change the numbers and predict each answer before you run it. Keep going until you stop being surprised.

Task 2: The Average That Is Not

Add this to the bottom of the same file:

1
local a = 80
2
local b = 90
3
local c = 100
4

5
print("Average: " .. a + b + c / 3)

Average: 203.33333333333

Three test scores of 80, 90 and 100, and it reports an average of 203. Work out on paper what it actually calculated, write that on your sheet, then fix the line with parentheses and check you get 90.

Task 3: Seconds Into Minutes

Copy the template to 1-05-time. This one asks a question, so it needs tonumber from last session:

1
io.write("How many seconds? ")
2
local total = tonumber(io.read())
3

4
local minutes = math.floor(total / 60)
5
local seconds = total % 60
6

7
print(total .. " seconds is " .. minutes .. " minutes and " .. seconds .. " seconds.")

How many seconds? 500 [Enter]
500 seconds is 8 minutes and 20 seconds.

Test it with 500, then 60, then 59, then 3600. Write down what it says for each.

Challenge (Optional): Break It on Purpose

Divide by zero:

print(10 / 0)

inf

No error. inf is short for infinity, and it is a value like any other — you can store it, print it, and add to it. Try print(10 / 0 + 5) and write down what you get.

Every other language you meet will do something different here. Several of them crash.

Challenge (Optional): Change for a Dollar

Write a program that asks for a number of cents and answers with how many quarters, dimes, nickels and pennies to hand back — largest coins first. 117 cents is 4 quarters, 1 dime, 1 nickel and 2 pennies.

You have everything you need: math.floor for how many fit and % for what is left.

Same Idea, Exam Notation

The arithmetic on the exam is the arithmetic you just did. The operators are the same and so is the order of operations.

local total = tonumber(io.read())

local minutes = math.floor(total / 60)
local seconds = total % 60

print(minutes)
print(seconds)

total ← INPUT()

seconds ← total MOD 60
minutes ← (total - seconds) / 60

DISPLAY(minutes)
DISPLAY(seconds)

Three differences worth knowing

• There is no math.floor on the exam, and there is no rounding operator at all. To drop the decimal you subtract the remainder first, then divide — which is what the right hand column above does.
• There is no ^ on the exam. A power has to be written as repeated multiplication.
• DISPLAY puts a space after what it shows. Two of them in a row give you space-separated output, not two things jammed together. This matters on trace questions.

Checkpoint

• All six operator results are written on your sheet
• You can say what the broken average line actually calculated
• 1-05-time is correct for 500, 60, 59 and 3600
• You can point at the line that gives whole minutes and the line that gives leftover seconds

Reflection

Answer the following questions before submitting your work.

1. The broken average printed 203.33333333333 instead of 90. Explain, step by step, what the computer did with a + b + c / 3 and why it is not a bug in Lua.
2. math.floor(total / 60) and total % 60 answer two different questions about the same number. Say what each one answers, in words, without using the word divide.
3. Dividing by zero printed inf and did not stop the program. Describe a situation where that is worse than crashing.

Submit

Submit the required files to the appropriate dropbox.

Activity Complete