Computers are most useful when you can use a small amount of code to $*$do the same action$*$ to $*$many different things$*.$

For example, in the time it takes you to calculate the $18\%$ tip on a restaurant bill, a laptop can calculate $18\%$ tips for every restaurant bill paid by every human on Earth that day. $($That$\text{'}$s if you're pretty fast at doing arithmetic in your head!$)$

$**$Arrays$**$ are how we put many values in one place so that we can operate on them as a group. For example, if $`$billions$\_$of$\_$numbers$`$ is an array of numbers, the expression

$\mathrm{.}18*$ billions$\_$of$\_$numbers

gives a new array of numbers that contains the result of multiplying each number in $`$billions$\_$of$\_$numbers$`$ by $\mathrm{.}18.$ Arrays are not limited to numbers; we can also put all the words in a book into an array of strings.

Concretely, an array is a $**$collection of values of the same type$**.$