Coding classes in Caerphilly county borough

The learner saves the text of Cadw's record and writes a regular expression, a compact search pattern, that picks out every place where a number with an imperial unit is followed by a metric figure in brackets: inches with metres, feet with metres, tons with tonnes. For each pair, the program converts the imperial figure itself, one inch being 0.0254 metres and one foot 0.3048, and compares the result with the bracketed number. Anything more than 3 per cent apart is flagged for a human to look at. The program finds six pairs.

Four pairs agree to well within rounding. The cylinder figure does not: 42 inches works out at 1.067 metres, while the bracket says 1.4, almost a third more. The program cannot say which half is the slip, only that the two cannot both be right, which is exactly what a good checker should report. The tons are subtler. Britain's traditional long ton is about 1.016 tonnes and the American short ton about 0.907; the record's conversions multiply by 1.020, close to the long ton but not exact. Nothing is necessarily wrong here: rounded figures such as c 6,000 were converted roughly. But it shows why a program handling tons must ask which ton is meant.

The learner then makes the checker sturdier: it must cope with commas in numbers, with mm as well as m, and with a pair written the other way round. Each new rule gets a small test of its own, so that fixing one case never quietly breaks another.

Teenagers in Caerphilly should still learn to code in 2026 so they can make the machine check numbers instead of just repeating them. The longer argument is in why teenagers should still learn to code in 2026.