One of the most powerful aspects of computer programming is the
ability to process variable data to achieve a result. Regardless of
the complexity of a process, when data is unknown or varies, you substitute
a symbol for the data. This is much like substituting
x and
y in an algebraic equation.
x = y + 29
The symbol, when its value can vary, is called a variable. A group of symbols or numbers that must be calculated to be
resolved is called an expression.