Beginner tutorial

These lessons are for someone new to programming. You will write a temperature report using sample readings, so you need a computer but no sensor or ESP32. If you already program, start with Toit for programmers.

You should be comfortable creating a text file and opening a terminal. The terminal is where you type the command that runs your program. We explain the programming concepts as they appear.

Each example is a complete program. Replace the contents of your file rather than appending the example to the previous one. Run it after each change.

1. Run your first program

Install the Toit SDK, which includes the tools to run Toit programs. Check the installation by typing toit --help in a terminal. It should display instructions for the command. If you already have Jaguar installed, use jag toit instead of toit in these commands; you do not need to connect a device.

In a text editor, create a file named report.toit containing these two lines:

main:
  print "Temperature report"

The two spaces before print matter. Use spaces, not the Tab key. Save the file, open a terminal in the directory containing it, and type:

toit run report.toit

You should see:

Temperature report

main: marks where the program starts. The indented line underneath it is an instruction: print displays the text between the double quotes. Text written this way is called a string. The quotes are part of the program, but are not printed.

Change Temperature report to Kitchen report, save, and run the command again. The new message should appear. The program runs the saved version of your file, so remember to save before running.

2. Give a value a name

We want the report to include a temperature. We could print 21 directly, but naming it lets us use the same value in several places.

A variable is a name for a value. temperature := 21 creates a variable named temperature with the value 21. The := introduces that new name.

main:
  temperature := 21
  print temperature

This prints 21. There are no quotes around temperature: we want its value, not the word “temperature”. Instructions run from top to bottom, so the variable is created before print uses it.

Change 21 to 24, save, and run again. Then try print "temperature" and compare the output. Put print temperature back before continuing.

3. Change the value

Once a variable exists, use = to replace its value. Use := only when introducing the name.

main:
  temperature := 21
  print temperature
  temperature = 24
  print temperature

The output is:

21
24

The first print uses the value at that point in the program. Changing the variable later does not change text that has already been printed.

You can calculate a new value from the old one. Replace temperature = 24 with temperature = temperature + 3. Toit first adds three to the current value, then stores the result. The output should stay the same.

Try adding five instead. Predict the second line before running the program.

4. Put the value in a message

To print a label and a value together, put $temperature inside a string. Toit replaces it with the variable's value. This is called interpolation.

main:
  temperature := 21
  print "Temperature: $temperature C"

This prints:

Temperature: 21 C

Change the value to 24. You only need to change the line that sets the temperature; the message uses that value automatically.

5. Decide what to print

Our program should say “Warm” when the temperature is at least 25 degrees. Otherwise, it should say “Comfortable”. The question “is this temperature at least 25?” is written as temperature >= 25.

main:
  temperature := 24
  print "Temperature: $temperature C"
  if temperature >= 25:
    print "Warm"
  else:
    print "Comfortable"

This prints:

Temperature: 24 C
Comfortable

if asks the question. When the answer is yes, the program runs the further indented instruction below it. When the answer is no, it runs the instruction below else: instead. Only one of the two messages is printed.

The comparison is called a condition. Its result is true for yes or false for no. Those two values are called booleans.

Try temperatures of 25 and 30. Both should print Warm. Try 20, which should print Comfortable. You have now checked values below, at, and above the threshold.

Practice before continuing

Change the report so that it describes a freezer: print Freezing when the temperature is below zero, and Not freezing otherwise. Use < for “less than”. Check the program with -5, 0, and 5.

You have a complete program that stores a reading, includes it in a message, and chooses a description. Continue with lists and functions to report several readings without copying the same instructions for each one.