Summary

In this lesson, you learned that:

A variable is a name for a value: local coins = 120. = means “store”, not “equals”. You write local once, when you create the variable; without it, Lua creates a global variable. In this course, every variable is local.
Names contain the letters a to z, digits and _, don't start with a digit, and can't be keywords. Uppercase and lowercase letters matter. This course writes them in camelCase: seedPrice.
You change a variable by storing a new value in it, often calculated from the old one: coins = coins + 5. Standard Lua has no += or ++.
Numbers are integers (5) or floats (5.0), and floats are written with a decimal point. / and ^ always give a float, // divides and rounds down, and % gives the remainder. math.type tells you which kind a number is.
math.floor and math.ceil round down and up and return integers; math.floor(x + 0.5) rounds to the nearest whole number. math.max, math.min and math.abs return the largest value, the smallest value and the absolute value.
Texts (strings) go in "…" or '…'. \", \n and \t are a quote, a new line and a tab. .. joins texts without adding spaces, and # gives the length in bytes.
nil means no value. A variable without a value, and a name with a typo, give nil, and joining or calculating with it is an error. (local 'x') in the message means a variable without a value, (global 'x') usually a typo.
true and false are booleans. type returns the type of a value as a text: "number", "string", "boolean", "nil".
tonumber turns a text into a number, or returns nil if the text isn't one; tostring turns any value into a text. Lua converts some texts to numbers by itself, but don't rely on it.
string.format builds a text from a template: %d for a whole number, %.2f for two decimal places, %s for any value, %% for a percent sign.

In the next lesson, on conditions, your programs will learn to make decisions: to do one thing or another, depending on the values of variables.

Instructions

Before you go on, try it all out on Emma's evening report. Calculate how many full boxes Emma can fill with her eggs and how many eggs are left over, and print it like this:

Boxes: 4, eggs left: 3

Emma sells the full boxes for boxPrice each. Add the money to coins, and print coins with string.format and two decimal places:

Boxes: 4, eggs left: 3
Coins: 58.00

Grandpa Joe pays back the coins he owed Emma. The amount is in his note, joeNote, which is a text. Convert it with tonumber, add it to coins, and print coins with ... You'll see .0 at the end: coins became a float when you added the money for the boxes, because boxPrice is a float.

Boxes: 4, eggs left: 3
Coins: 58.00
Coins: 73.0

Emma writes only whole coins in her notebook. Print coins once more, with string.format and %d:

Boxes: 4, eggs left: 3
Coins: 58.00
Coins: 73.0
In the notebook: 73 coins

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10/10