Day 7 of 100 Days Coding Challenge: Python
Ah yes, the BMI calculator—a classic Python rite of passage. I built one last year when I was still figuring out how loops worked and thought elif was a typo. It worked… but only in metric. That was fine for me, having grown up in Japan and lived in Canada, where weight is measured in kilograms, height is measured in meters, and the weather is often cold.
But then I remembered: the U.S. exists. A land where temperature is measured in fractions of lava and weight in pounds that are somehow not British. Clearly, this app needed to accommodate both worlds—metric precision and imperial chaos.
So this time, I added a choice: metric or imperial. Because inclusivity matters. I even sprinkled a little personality into the experience—some clever text formatting, gentle prompts, and error handling. As a Japanese person, I believe that even software should have good manners.
Today’s Motivation / Challenge
The challenge today wasn’t just writing a BMI calculator—it was writing one that respects cultural measurement quirks. The metric system is excellent, but millions of people use the imperial system, and they deserve not to be confused. More importantly, this was an opportunity to practice user input, conditionals, and conversions—all critical building blocks in a beginner’s coding toolkit. And let’s be honest: anything that turns body mass into a friendly number is kind of fun.
Purpose of the Code (Object)
This app calculates your Body Mass Index based on your weight and height. You choose whether to use the metric system (kilograms and meters) or the imperial system (pounds and inches). Behind the scenes, the code converts everything into metric and then applies the BMI formula. The result? A simple number—and a label—that gives you a rough idea of your body composition.
AI Prompt
Write a Python app that asks users to choose metric or imperial units, collects weight and height, converts if needed, and calculates BMI with a health category.
Functions & Features
- Prompts user to choose between metric and imperial units
- Collects weight and height accordingly
- Converts imperial inputs to metric for calculation
- Calculates BMI using the standard formula
- Classifies the result (underweight, normal, overweight, or obese)
- Includes input validation with try/except to handle typing hiccups
Requirements / Setup
- Python 3.x
- No external libraries needed (runs with pure Python)
Minimal Code Sample
python
CopyEdit
if unit == “imperial”:
weight_kg = weight_lbs * 0.45359237
height_m = height_in * 0.0254
bmi = weight_kg / (height_m ** 2)
This snippet handles unit conversion and calculates BMI.
Notes / Lessons Learned
By the way, I used try/except to catch input errors because I care about user experience—and also because I’ve personally broken every beginner app by typing “ten” instead of “10.” It’s a small thing, but it saves users (and me) a lot of head-scratching.
And yes, the final BMI result pops out like a helpful robot telling you how dense you are… in the kindest possible way.
Could I have just said, “Google your BMI”? Sure. But where’s the fun in that? Now I’ve got a custom-built BMI calculator that speaks both metric and imperial, politely handles mistakes, and makes me feel like an international coder of mystery.
Posted it on GitHub, naturally. Another green dot was added to the timeline. I still haven’t cleaned up the repository names, but hey—that’s a Day 30 problem.
Day 7: BMI balanced. Unit confusion conquered. Nerd pride: fully intact.
Optional Ideas for Expansion
- Add age and gender inputs to adjust health ranges
- Build a GUI version using Tkinter for a more visual experience
- Allow saving BMI history to a text or CSV file for tracking progress