# Daily Challenge #57 - BMI Calculator

### dev.to staff ・1 min read

Daily Challenge (161 Part Series)

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Write a function that calculates body mass index

Note: bmi = weight / height ^ 2

if bmi <= 18.5 return "Underweight"

if bmi <= 25.0 return "Normal"

if bmi <= 30.0 return "Overweight"

if bmi > 30 return "Obese"

*This challenge comes from wichu on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!*

*Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!*

Classic DEV Post from Jun 14 '19

Well, I tried something different:

Apart from being ugly, it works like this:

`t=[18.5,25,30]`

`k=['Underweight','Normal','Overweight']`

`t.find(v=>w/(h^2)<=v)`

. For example, it will return`25`

if the processed BMI is between 18.5 and 25.`t.indexOf(...)`

, in order to get the same element in the label array:`k[...]`

. For example, if`25`

is returned, it will fetch`k[1]`

, hence`"Normal"`

`"Obese"`

That is an interested method, but come back at your code in a few months with absolutely no explanation and I do think that it is not going to be that easy.

I think that a code should be self explanatory (especially to newcomers on your codebase) and, even if this one is a tour-de-force in terms of one-liner, it is not self explanatory. 😉

That is why, I would find that a switch case method would be better.

I completely agree with you on this one! (Hi fellow french dev!) I tend to try to golf a lot in these challenges, even though I completely agree on the fact that it's as ugly as it can be. That way, I can discover new principles (like the

`reduce`

method, that I hated a few months back even if it is really useful) that I can later use on my projects or at work.Indeed, this challenge was clearly made for a switch/case solution, but as I had some free time I though I could try something different haha

I like it!

LabVIEW: ;)

Awesome, haven't seen LabVIEW since I was at uni.

Haskell

This seems to do the job

C++:

Might propose a change? Instead of underweight, overweight, obsese, etc, how about we replace the return values with "no idea, consult a health professional and have your body composition correctly measured"? It will be significantly more accurate! :D

Something like:

I concur with this response.

I couldn't resist posting a quick JavaScript solution... 😀

F#:

When reading the problem description I wasn't 100% sure which units the weight and height were supposed to be in. I googled and found both a metric and imperial definition, so I decided to use units of measure and nested modules so callers of the code need to be explicit. Example:

The active pattern

`LessOrEqual`

was purely for fun, one could just use`if-else`

expressions or pattern matching with guards.Rust:

Let's say you need to run this a few billion times times, then a more complex look up table approach might be worth it.

(in JS because I like it, and I find it can be nice to mock up performance code in a slowish language first up.)

Have you tested if your code is faster than a simpler conditional version (as most other solutions are written)?

Fair point Craig, in this case it turns out to be a bunch slower due to the complexity in

`indexFromBmi`

.I just figured it was worth posting as an alternative approach as there are problems where luts are gold. In this case apparently not.

I'd say that here it's best to just use

and be done with it.

A solution in gwion

Scala:

rust:

I did two functions, one that expects imperial units (Go America!) and one that expects metric units (the rest of the world!).

body.go

body_test.go

[gist.github.com/devparkk/9117b0780...]