The simplest difference I see between an Expression and a Statement
is that Expressions calculate something, and Statements merely state
that something has a particular value. Any value which is calculated
is an Expression. X+5 is an expression, X=5 is a Statement.
When you see the '=' sign in programming it does not mean the same
thing as it does in Math.
In programming it means that whatever the value is to the right of the
equal sign,
is now to be placed into the Variable Name on the left side of the equal
sign.
In Math
Payroll = Payroll + $40.00 could not be true.
(Something numeric cannot have the same value as itself plus any non
0 value.)
But in Programming
Payroll = Payroll + 40 means that you caculate the value of Payroll
+ 40
and place that value into the memory location known as Payroll.
(The value of what is to the right of the = goes into the Variable on
the left.)
So is Payroll = Payroll + 40 a Statement or an Expression?