A quick latex programming tutorial
So, I like LaTex. Itâs like programming a document and having (nearly) full control about what happens with lots of fancy packages. I came across the Tikz-Package (which allows you to even programprogram graphics) I also found this brilliant documentation (which you can find here, if youâre interested http://pgfplots.sourceforge.net/TeX-programming-notes.pdf ) So I got to the point where I was able to automatically attach the fraction labels with a foreach loop.Â
That was the point where I thought that it would be nice if I could write a little program to simplify the fractions and display integers where possible. As it seems not to be the most natural thing to do with LaTex (I spent some time on research) as you can use things like R and Sweave and whatever (Iâm just a newbie to LaTex - thatâs why I wanted something simple) it took me some time to figure it out. So, letâs get started!
As in any procedural language you find different types of variables you can use. However, by default, they seem to be limited and not changeable in their names. So if you want to store an integer you type \count0=1 where â\countâ tells LaTex that itâs an integer and the number 0 to use the first of the 256 available slots, followed by an equal sign and the value you want to store within (the length of the number you can store is 32 bit). There are also 256 \dimen (fixed point numbers which need a unit behind like pt or cm) and \toks (string), always followed by the number of their register.
You can display the value of these variables by adding a \the before their name. so
The answer to eveything is \the\count0 .Â
Will produce the output âThe answer to everything is 42.âÂ
Surprise! Well that was easy. Letâs move on to...
Letâs suppose you want to compare your variable to another number. What you would type is:
 This is a positive number.
 This is a negative number. Or 0.
You can do the same thing with \dimen by typing \ifdim. You may say: âThatâs nice, but what about logical operators like âANDâ or  âORâ?â and the sad answer is, I donât know. There might be packages that implement an \or - but you have to find them yourself - I didnât. So what to do. At least you can nest the if statements, so that if you wanted to know if your number is greater than 10 and smaller than 20 it would look like this:
    \count0 is smaller than 20 AND greater than 10.
Ok, but...what about booleans? Do I have to use integers and compare their value? Well you âonlyâ have 256 that all have the same name so luckily there are Booleans. I didnât mention them in the variable part - thatâs because they seem to be made explicitely for if statements (ok what other purpose would have a boolean). You can even give them names. You declare them by \newif\ifnameofthevariable and set them by \nameofthevariablefalse or \nameofthevariabletrue.Â
 this will never happen.
 this will be displayed.
Crazy stuff and not the language you want to program a rocket launcher with. Still some things left to cover. For example...
3 (Builtin) Arithmetical operations
Suppose you want to add 10 to your variable. You have to do this:
same applies to division (\divide) and multiplication (\multiply). Ah yes. and there is no subtraction. You can however abuse the âadvanceâ operator and add a negative number.Â
Or you agree with me that this is poor and use a package. Like intcalc. So we declare \usepackage{intcalc} at the beginning of our document and can do nearly ârealâ math ;-) you can view the documentation here. There is also a nice function for Subtraction.
You can comment at any time in Latex by Starting with a %.
I donât know if the original idea behind this command was to allow functions, but it does. \newcommand{\nameoffunction}[2]{%stuffthatthefunctiondoesgoeshere} defines a function that is called ânameoffunctionâ and that has 2 arguments. The first function call is always behind the declaration of the function. Meaning that calling the function before its declaration wonât work. It is therefore a good idea to place the function declarations and its definition at the top of your document. An example of a function I will provide in the following chapter.
For my case of the simplification of fractions I needed to have a loop. There is no basic concept again, meaning you could use a construct like for (int i; i<10;i++) do something. You can create yourself loops to what you need. There is this pdf online to show you how (and which I used to learn most of the programming features of latex)
In my case, I simply did a recursion right away:
%Returns greatest common divisor %#1 must be greater than #2
  \euclid{#2}{\intcalcMod{#1}{#2}}
The greatest common divisor of 256 and 96 is \euclid{256}{96}
---Â
With all that stuff learnt, I finally got my labeling to work :-)
\newcommand{\fracOrNot}[2]
\ifnum#1=\intcalcAbs{#1} %1 is positive
\ifnum#2=\intcalcAbs{#2} %2 is positive
\ifnum#2=\intcalcAbs{#2} % 2 is positive
\ifnum\intcalcAbs{#1}<\intcalcAbs{#2}
%first number must be greater than 2nd number
\count3=\intcalcDiv{\count0}{\euclid{\count0}{\count1}}
\count2=\intcalcDiv{\count1}{\euclid{\count0}{\count1}}
\count2=\intcalcDiv{\count0}{\euclid{\count0}{\count1}}
\count3=\intcalcDiv{\count1}{\euclid{\count0}{\count1}}
$-\frac{\the\count2}{\the\count3}$
$\frac{\the\count2}{\the\count3}$
  \euclid{#2}{\intcalcMod{#1}{#2}}
\newcommand{\simplify}[2]{
%if one of the arguments is 0, return 0
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