Amy McMullin

Amy McMullin

she/her

Bringing 25 years of IT experience to the classroom

PHP Temperature Gradient

LIS 5367 Advanced Web Applications, M.S. Information Technology, Florida State University — Summer 2021

See it running →

The exercise

Build a Fahrenheit-to-Celsius conversion table in PHP. At least 100 rows, Celsius accurate to a tenth, and at least three named temperature bands — the instructor left the band names and thresholds to us. Three sub-problems: arithmetic in PHP, a finite incrementing loop, and selecting a description based on a numeric range.

Then two optional extensions, offered for nothing but bragging rights:

  • Bonus — color each description by its band. Hot red, cold blue.
  • Super bonus — give every line its own color, slightly different from the ones above and below, producing a smooth gradient from deep blue at the cold end to bright red at the hot end.

Why the super bonus is the interesting one

The base exercise is a loop and a conditional. The super bonus is a different kind of problem: it needs a continuous mapping from one range onto another.

The bands are discrete — a row is COLD or NICE or HOT, nothing in between. But the gradient has to be continuous across all 101 rows, which means per-row color can’t come from the band at all. You have to interpolate: normalize each temperature to a position between 0 and 1 across the full range, then interpolate the red and blue channels across that position and emit the result as a hex value, every row, inside the same loop that’s already doing the conversion and the band lookup.

So one pass through the loop produces three things computed three different ways — an arithmetic conversion, a discrete lookup, and a continuous interpolation. For a first semester of PHP that’s a genuinely good exercise, and I remember it being the first time the language stopped feeling like filling in a template.

I set my bands at COLD below 65°F, NICE from 65 through 85, and HOT at 86 and above.

The super bonus submission: a 101-row conversion table shading from blue through to red

Submissions

All three are still live on FSU’s Torch server, five years on:

A caveat on the last two: they currently render the table structure and the band labels but not the numeric values. I no longer have access to the account, so I can’t read the source to say whether those two were always incomplete or whether something broke under a later PHP version. The super bonus submission still renders correctly, which is the one I’d have spent the most time on.

The larger project from this course was the iTech Differentiated OCP Tracker.