Values and variables

By the end of this step you can store information in a program, do sums with it, and print it.

Values come in kinds

Programs work with values. The three you'll use most:

Quotes matter: "42" is text that happens to look like a number. 42 is a number you can do maths with.

Variables are labelled boxes

A variable is a name for a value, so you can use it later. Think of a box with a label on it:

Read = as "store", not "equals": store 249.99 in the box called price.

JavaScript adds a word in front. const means "this box won't change". let means "this box might change later". Python doesn't bother.

Names are up to you, but no spaces. Python style joins words with underscores (in_stock); JavaScript style uses capitals (inStock). Same idea, different habit.

Try it

Read the code first, top to bottom, and guess what each line will print. Then press Run and check your guesses.

# A variable is a name for a value. The = sign means "store this value under this name". product = "Trail Tent" # text (a "string"): always in quotes price = 249.99 # a number in_stock = True # true or false (a "boolean") print(product) print("Price:", price) print("In stock?", in_stock) # You can do maths with numbers... with_tax = price * 1.08 print("With tax:", round(with_tax, 2)) # ...and join text together. str() turns a number into text first. label = product + " costs $" + str(price) print(label) # Your turn: add a variable called quantity, set it to 3, # then print how much 3 tents cost.

Output

Press Run (or Ctrl+Enter) to see the output here.

// A variable is a name for a value. "const" means "store this value under this name". const product = "Trail Tent"; // text (a "string"): always in quotes const price = 249.99; // a number const inStock = true; // true or false (a "boolean") console.log(product); console.log("Price:", price); console.log("In stock?", inStock); // You can do maths with numbers... const withTax = price * 1.08; console.log("With tax:", withTax.toFixed(2)); // ...and join text together. Backticks let you drop values into text with ${ }. const label = `${product} costs $${price}`; console.log(label); // Your turn: add a variable called quantity, set it to 3, // then print how much 3 tents cost.

Output

Press Run (or Ctrl+Enter) to see the output here.

A few things to spot:

• Lines starting with # (Python) or // (JavaScript) are comments: notes for humans. The computer skips them.
• price * 1.08 is maths: * multiplies, / divides, + adds, - subtracts.
• Joining text needs care. In Python, "costs $" + 249.99 is an error: you can't add text to a number. str(price) turns the number into text first. JavaScript's backticks (`) let you drop values straight into text with ${ }.

Want to see an error on purpose? In the Python box, remove str( ) around price and run it. Read the last line of the error: it tells you exactly what went wrong. Then press Reset.

Your turn

At the bottom of either box: add a variable called quantity set to 3, then print how much 3 tents cost, with tax.

Show a hint (1 of 3)