RecursionThe two parts every recursive function needs, and when to avoid it.ComputingEvery correct recursive function has exactly these parts.1The base caseThe smallest input, answered directly with no further calls.2The recursive caseReduce the problem, call yourself, combine the result.3Guaranteed progressEach call must move measurably toward the base case.FACTORIALif n <= 1: return 1return n * factorial(n - 1)Progress: n decreases every callEach call costs a stack frame. Depth beyond a few thousand overflows;rewrite as a loop or add memoisation.Recursionlearnposters.com
Recursion — printable computing wall chart from LearnPosters. Free vector PDF, US Letter and A4.

Recursion, step by step

Every correct recursive function has exactly these parts.

  1. The base caseThe smallest input, answered directly with no further calls.
  2. The recursive caseReduce the problem, call yourself, combine the result.
  3. Guaranteed progressEach call must move measurably toward the base case.

Factorial

  • if n <= 1: return 1
  • return n * factorial(n - 1)
  • Progress: n decreases every call

Each call costs a stack frame. Depth beyond a few thousand overflows; rewrite as a loop or add memoisation.

Questions about the Recursion poster

What’s on the Recursion poster?
3 numbered steps, with a full worked run-through. Every correct recursive function has exactly these parts. The base case — The smallest input, answered directly with no further calls.; The recursive case — Reduce the problem, call yourself, combine the result.; Guaranteed progress — Each call must move measurably toward the base case.. Each call costs a stack frame. Depth beyond a few thousand overflows; rewrite as a loop or add memoisation.
Who is the Recursion poster for?
Recursion belongs to the Computing section rather than to a school year, because computing is not something one grade owns. Anyone learning foundations can pin it up — a beginner, a student mid-course, or someone revising years later.
When should you use the Recursion poster?
Write the base case first. A recursion without one is an infinite loop with extra steps. A wall chart earns its place by being glanceable from where the work is happening, so Recursion belongs on the wall where that computing work actually happens, within glancing distance, rather than filed away.
What other posters go with Recursion?
Big-O Complexity, Binary, Hex & Decimal and Bits, Bytes & Sizes sit alongside Recursion in the Computing section. Printed together they make a wall rather than a single sheet, which is how a reference set actually gets used.Big-O ComplexityBinary, Hex & DecimalBits, Bytes & Sizes
Is the Recursion poster free to download and print?
Yes. Recursion downloads as a free PDF with no account, no email and no watermark, like everything else in the Computing section. Print as many copies as you like for a home, a classroom, a library or a tutoring group; reselling the file is the only thing the licence rules out.Read the licence
What size does the Recursion poster print at?
Recursion is a vector PDF laid out for US Letter, and prints on A4 with Fit to page — the same file, no separate download. Because every mark on it is drawn rather than photographed, it stays sharp enlarged to A3, A2 or A1 at a copy shop. Colour carries emphasis only, so a greyscale print of Recursion loses nothing.Printing guide

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