A till receipt on a paper roll

A counter till prints on a roll 80 mm across, and a roll has no bottom edge: the paper is cut where the basket ends. So the page is as long as what was bought, and not a figure on it is written down beforehand. A line comes to its quantity times its unit price, the tax at each rate is taken out of the gross that carries it, and the change is what is left of the note handed over. Ring up one article more and the roll grows by one line, with the totals still under it.

The barcode at the foot is what the shop scans when the ticket comes back — a return, an exchange, a warranty claim. Nothing chooses its code set by hand: the library reads the ticket number, finds nothing in it but digits, and packs it two digits to a symbol, 112 modules where spelling the number out character by character would take 189. Whether it scans is for a scanner to say, and one does say: a decoder is pointed at the rendered page and reads the number back.

What this example shows

• A roll 80 mm across, cut as long as the basket makes it.
• Six articles, the tax gathered by rate, and the change worked out from the note handed over.
• The ticket number carried as a barcode, in the code set the library picks for it.

The source code, complete

Nothing is left out and nothing is simplified: this is the program exactly as it runs, for whoever writes your software.

Read the Rust source Read the Python source

The document itself

Open the document in English Open the document in French

This document weighs 17.3 kB

See the size of every example document.