What is a Variable?

A variable is a symbol that represents a number you don't know yet. You use letters like $x$, $n$, or $k$ to stand in for values.

For example, if you have $x + 5 = 12$, the variable $x$ represents some number that makes this equation true. Your job is to find what $x$ equals.

In programming, variables are everywhere. Array length $n$, loop counter $i$, time complexity $T(n)$. Algebra teaches you how to work with these symbols before you know their values.