Countdown

A rocket counts down from ten. Read the program and guess what it prints before you run it.

This is your first text. A rocket is about to start, and the program counts down to the launch.

Before you run it

Read the program and write down what it prints, line by line. Pay attention to the last three numbers.

The text

my $rocket = 'Vostok';

say "Rocket $rocket is ready.";

for 1..10 {
    my $left = 11 - $_;
    if $left > 3 {
        say $left;
    }
    else {
        say "$left!";
    }
}

say 'Lift-off!'.uc;

Rocket Vostok is ready.
10
9
8
7
6
5
4
3!
2!
1!
LIFT-OFF!

Words

• my — creates a new variable. A variable that holds one thing has a name that starts with $.
• say — prints something and goes to the next line.
• for — repeats the block in { } once for every value in a list.
• 1..10 — a range: the numbers from 1 to 10.
• $_ — the current value inside a for loop: 1 the first time, 2 the second, and so on.
• if, else — run one block or the other, depending on a condition.
• .uc — gives the string in upper case.

Reading notes

my $rocket = 'Vostok';
say "Rocket $rocket is ready.";

The first line puts the name Vostok in the variable $rocket. In double quotes, a variable is replaced by its value, so the second line prints Rocket Vostok is ready. In single quotes, it would print the name of the variable as it is.

for 1..10 {
    my $left = 11 - $_;

The loop runs ten times, with $_ going from 1 to 10. The program wants to count down, not up, so it calculates $left: 11 − 1 = 10 the first time, 11 − 2 = 9 the second time, and 11 − 10 = 1 the last time.

    if $left > 3 {
        say $left;
    }
    else {
        say "$left!";
    }

While more than three seconds are left, the program prints the number. For 3, 2 and 1, it prints the number with an exclamation mark.

say 'Lift-off!'.uc;

The last line runs once, after the loop. .uc turns Lift-off! into LIFT-OFF!. Only letters change; the hyphen and the exclamation mark stay.

Questions

1. How many lines does the program print?
2. Which line would change if the rocket were called Soyuz?
3. What would the program print if the condition were $left > 5?

Try this

Make the rocket count down from 20 instead of 10. You need to change two numbers. Which ones, and why both?