hello

> examples hello
> edit hello

The very first program: it asks for your name, says hello, counts down from 3 and invites you to edit it. It shows the three functions every program uses sooner or later: print to show a line, read to get what the player types, and sleep to wait.

#What to build

Nothing: hello only uses the screen and the keyboard, on any computer. The first program tutorial walks through it step by step.

> examples hello
> hello
What is your name? Steve
Hello, Steve!
3...
2...
1...
Edit me: edit hello

#How it works

write("What is your name? ")
local name = read()

write shows text without going to the next line, so the cursor waits right after the question. read() then pauses the program until the player presses Enter, and gives back the line typed, as a string. While it waits, the computer spends no instructions. The answer goes into a local variable called name.

print("Hello, " .. name .. "!")

.. glues strings together. print writes the result and goes to the next line.

for i = 3, 1, -1 do
  print(i .. "...")
  sleep(1)
end

A for loop with a third number: i starts at 3, goes down by 1 (the -1), and stops after 1. sleep(1) waits one second each time round.

#Ideas

• Count from 10 instead of 3, or count by twos. The third number of the for is the step:

  for i = 10, 0, -2 do
    write(i .. " ")
  end
  print("liftoff!")

  Screen

  10 8 6 4 2 0 liftoff!

• Handle an empty answer: after read(), add if name == "" then name = "stranger" end.
• Ask a second question (What do you build?) and use both answers in the greeting.
• Greet by the time of day: os.day_time() gives the time of the world, see the clock example.
• Make it a door greeter: put it in startup with a while true do ... end around it, on a computer by your front door.

#The program

-- Your first program. Run it by typing its name: hello
-- print() writes a line, read() waits for what you type.
write("What is your name? ")
local name = read()
print("Hello, " .. name .. "!")
for i = 3, 1, -1 do
  print(i .. "...")
  sleep(1)  -- waits one second
end
print("Edit me: edit hello")