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3. Conditions and Loops

Level: beginner · Reading time: 3 min · Prerequisite: book/poche/02-variables-and-types.html · Last review: 2026-05-09

TL;DR (5 lines)

  • Read the core idea first.
  • Understand one concept at a time.
  • Run small examples.
  • Fix errors early.
  • Move to next chapter only when clear.

Frequent mistakes

  • Skipping prerequisites.
  • Reading without trying examples.
  • Fixing too many errors at once.

Prerequisites: book/poche/02-variables-and-types.html. See also: book/chapters/07-control.html.

Goal

Choose a path (if) and repeat an action (loop/for).

Example

entry main at app/demo {
  let n: int = 3
  if n > 0 {
    return 1
  }
  return 0
}

Why it matters

Flow control is the central logic of a program.

Quick check

What output do you get if n = 0?

Try this

  1. Edit condition.
  2. Test 3 input values.
  3. Note the exits.

If you're stuck

Always write the nominal case first, then the limiting case.

Mini quiz

  1. What is the main goal of this chapter?
  2. Which concept is most important?
  3. What will you try right now?

See also

Next best action

Apply one idea from this chapter in a tiny example, then continue.