Showing Your Work

So far the computer has shown you words you typed between quotation marks. Now it shows you something it works out for itself.

Text, or a value

Look at these two instructions. They are almost the same. One has quotation marks and one does not.

SHOW "2 + 2"
SHOW 2 + 2

2 + 2
4

The quotation marks decide the meaning. Inside them, 2 + 2 is text, and the computer shows it letter for letter. Outside them it is a sum, and the computer works it out.

The machine is not guessing. You chose which one you meant by how you wrote it.

Joining text to a value

A bare 4 does not tell you much. Usually you want to say what it is, so you join some fixed text to the value:

SHOW "Two plus two is ", 2 + 2

Two plus two is 4

The comma joins one thing to the next. It adds nothing of its own: no space, no punctuation. If you want a space before the 4, put it inside the quotation marks, the way "Two plus two is " does above.

That join is what makes output readable. Score: 100, You have 3 lives left and Time: 42 are all a piece of fixed text with a value joined on.

When it’s wrong, see why

• You see 2 + 2 where you wanted 4. The sum sits inside quotation marks, so the computer showed it as text. Take the quotes off the part you want it to work out.
• You see a bare number with nothing to explain it. Join some text on to say what it is.
• The text runs into the number, like Two plus two is4. The space belongs inside the quotation marks. The computer shows exactly what sits between them.

What you’ve learnt

• Output can show a value the computer works out, not only fixed text.
• Quotation marks choose the meaning. Inside them it is text. Outside them the computer works it out.
• Joining text to a value makes output readable, and the comma adds nothing of its own.

What’s next

The computer can work a value out and show it. The moment it has shown it, it forgets it. In Unit 4 we give the program a memory.