1. The same program, both ways

Unit A · From blocks to text

The same program, both ways

What we are making: the blink from Level 1 — identical circuit, identical behaviour — but typed instead of dragged.

Photo: Arduino with a breadboard LED lit, laptop showing the Arduino IDE

The idea

We are deliberately starting with something you already know how to do. That way the circuit, the behaviour and the goal are all familiar, and the only new thing in the room is the language.

You are also swapping editors. mBlock goes away; from now on you use the Arduino IDE, which is what professionals use for these boards.

💡 Tip

Open last year's blink program in mBlock and look at it while you type this one. Find each block in the text. Everything maps across — nothing has been added or removed.

Side by side

Here is the whole program, both ways. Read across, row by row.

The block you already know

The line that does the same thing

when green flag clicked

void setup() {

set pin 9 to output

pinMode(9, OUTPUT);

}

forever

void loop() {

turn on pin 9

digitalWrite(9, HIGH);

wait 1 seconds

delay(1000);

turn off pin 9

digitalWrite(9, LOW);

wait 1 seconds

delay(1000);

}

Nine blocks, nine lines. Nothing was added and nothing was taken away.

The green flag became void setup(). Both mean 'do this once, at the start'.
The forever block became void loop(). Both mean 'do this over and over until the power goes'.
The C-shape that wrapped the blocks became the curly brackets. Same job: holding things inside.
The white ovals became the numbers in round brackets.
And every instruction gained a semicolon, because text has no edges to show where a line stops.

💡 Tip

The indenting — the two spaces before the inside lines — does nothing at all to the program. It is purely so humans can see what is inside what, the way the C-shape used to show you. Do it anyway. Code without it is unreadable.

Wire it up

Arduino board

Breadboard

LED

Resistor 220Ω

Jumper wires

Exactly the Level 1 Session 2 circuit. Nothing has changed.

Pins used9GND

Set up the editor

Open the Arduino IDE.
Go to Tools → Board and choose Arduino Uno.
Go to Tools → Port and choose the port your board is on. On Windows it looks like COM3; on a Mac it starts with /dev/cu.
You will see a file already containing an empty setup() and loop(). That is the skeleton — the two blocks from the comparison above, waiting to be filled.

🔧 If it goes wrong

If Port is greyed out, the board is not talking to the computer. Almost always a charge-only USB cable. Swap the cable first.

The code

Type this. All of it, by hand.

Your program

1void setup() {

2 pinMode(9, OUTPUT);

5void loop() {

6 digitalWrite(9, HIGH);

7 delay(1000);

8 digitalWrite(9, LOW);

9 delay(1000);

10}

Line by line

Line 1 — void setup() starts the block that runs once at power-on.
Line 2 — pinMode(9, OUTPUT) tells the board that pin 9 will be pushing electricity out, not reading it in. This had no block in mBlock; it was done for you invisibly.
Line 5 — void loop() is last year's forever block.
Line 6 — digitalWrite(9, HIGH) is 'set pin 9 to HIGH'.
Line 7 — delay(1000) is 'wait 1 second'. Milliseconds, so 1000 means one second.

⚠ Careful

pinMode is the one genuinely new idea here. In C++ you have to declare what a pin is for before you use it. Forget it and the LED will be very dim, or do nothing at all.

Try it

Click the tick to compile. This checks the text without sending anything to the board.
Click the arrow to upload.
Watch the LED.

What should happen: one second on, one second off. Exactly like last year.

🔮 Try this

Change delay(1000) to delay(100) and upload. Then make the on-time and off-time different, so it flashes like a heartbeat. You are now changing a program by editing numbers in text — which is much faster than finding blocks.

If it goes wrong

What you see	Why	What to do
'digitalWrite' was not declared in this scope	A spelling or capital-letter mistake.	It is digitalWrite — lower-case d, capital W. C++ is fussy about capitals.
expected ';' before '}' token	A missing semicolon on the line above.	Look at the line before the one named in the error.
Compiles fine, LED does nothing	pinMode is missing, or it is in the wrong way round.	Check line 2 is there, and that the long leg of the LED goes to pin 9.
Port greyed out or upload fails	Board not connected, or the wrong port selected.	Tools → Board → Arduino Uno. Then Tools → Port.

What you learned

Every program has setup() and loop(). They are the green flag and the forever block.
pinMode declares what a pin is for. Blocks did this for you.
Instructions end in a semicolon.
Indenting is for humans, not the computer. Do it anyway.
Blocks and text are the same thing wearing different clothes.

Challenge optional — only if you finish early

Take the blocks program and the C++ program and write, line by line, which block became which line. Every one.