Lesson 3 — Making decisions

You are here

1. Your first program ✓
2. Values and variables ✓
3. Making decisions ←
4. Repeating things
5. Functions
6. Lists and hashes
7. Strings
8. Organizing programs
9. Classes

What are we learning?

Programs often need to choose: do this, or do that.

In Echo, if means: if this is true, run the instructions inside { }.

Smallest useful example

age: int = 18;

if age >= 18 {
    say("Adult");
}

Output

Adult

Line by line

1. age holds the number 18.
2. age >= 18 asks: “Is age greater than or equal to 18?”
3. That question is true, so Echo runs what is inside { }.
4. say("Adult"); prints Adult.

If you change age to 15, the condition is false, and Echo skips the block — nothing is printed.

Adding an other choice: else

age: int = 15;

if age >= 18 {
    say("Adult");
} else {
    say("Under 18");
}

Output

Under 18

• If the condition is true → run the first block.
• Otherwise → run the else block.

Try it

Change age to 21 and to 10. Predict the output before you run.

Predict it

score: int = 50;

if score >= 60 {
    say("Pass");
} else {
    say("Retry");
}

Show answer

Retry

Fix it — missing braces

Echo needs { } around the instructions after if. This style is not allowed:

if true
    say("yes");

Use:

if true {
    say("yes");
}

Deeper (later)

else if, switch, and the full list of “false-like” values are in Control Flow (full).

Next

→ Lesson 4 — Repeating things