chapters/25.markdown @ efff67c5b753

Numbers
=======

Now it's time to start taking a closer look at the different types of variables
you can use.  First we'll go over Vim's numeric types.

Vimscript has two types of numeric variables: Numbers and Floats.  A Number is
a 32 bit signed integer.  A Float is a floating point number.

Number Formats
--------------

You can specify Numbers in a few different ways.  Run the following command:

    :::vim
    :echom 100

No surprises here -- Vim displays "100".  Now run this command:

    :::vim
    :echom 0xff

This time Vim displays "255".  You can specify numbers in hex notation by
prefixing them with `0x` or `0X`.  Now run this command:

    :::vim
    :echom 010

You can also use octal by starting a number with a `0`.  Be careful with this,
because it's easy to make mistakes.  Try the following commands:

    :::vim
    :echom 017
    :echom 019

Vim will print "15" for the first command, because "17" in octal is equal to
"15" in decimal.  For the second command Vim treats it as a decimal number, even
though it starts with a `0`, because it's not a valid octal number.

Because Vim silently does the wrong thing in this case, I'd recommend avoiding
the use of octal numbers when possible.

Float Formats
-------------

Floats can also be specified in multiple ways.  Run the following command:

    :::vim
    :echo 100.1

Notice that we're using `echo` here and not `echom` like we usually to.  We'll
talk about why in a moment.

Vim displays "100.1" as expected.  You can also use exponential notation.  Run
this command:

    :::vim
    :echo 5.45e+3

Vim displays "5450.0".  A negative exponent can also be used.  Run this command:

    :::vim
    :echo 15.45e-2

Vim displays "0.1545".  The `+` or `-` before the power of ten is optional. If
it's omitted then it's assumed to be positive.  Run the following command:

    :::vim
    :echo 15.3e9

Vim will display "1.53e10", which is equivalent.  The decimal point and number
after it are *not* optional.  Run the following command and see that it crashes:

    :::vim
    :echo 5e10

Coercion
--------

When you combine a Number and a Float through arithmetic, comparison, or any
other operation Vim will cast the Number to a Float, resulting in a Float.  Run
the following command:

    :::vim
    :echo 2 * 2.0

Vim displays "4.0".

Division
--------

When dividing two Numbers, the remainder is dropped.  Run the following command:

    :::vim
    :echo 3 / 2

Vim displays "1".  If you want Vim to perform floating point division one of the
numbers needs to be a Float, which will cause the other one to be coerced to
a Float as well.  Run this command:

    :::vim
    :echo 3 / 2.0

Vim displays "1.5".  The "3" is coerced to a Float, and then normal floating
point division is performed.

Exercises
---------

Read `:help Float`.  When might floating point number not work in Vimscript?

Read `:help floating-point-precision`.  What might this mean if you're writing
a Vim plugin that deals with floating point numbers?