An expression is a piece of code that produces a value of some kind. We’ve actually seen several examples already, the most basic being the numbers we’re assigning into the variables. So in our example, a number such as:

5.141

is an expression. Expressions where we just tell C# what value we
want are called *literal* expressions. More
interestingly, expressions can perform calculations. For example, we could
calculate the distance traveled per kilogram of fuel consumed with the
expression in Example 2-6.

Example 2-6. Dividing one variable by another

kmTravelled / fuelKilosConsumed

The `/`

symbol denotes
division. Multiplication, addition, and subtraction are done with `*`

, `+`

, and
`-`

, respectively.

You can combine expressions together too. The `/`

operator requires two inputs—the dividend and
the divisor—and each input is itself an expression. We were able to use
variable names such as `kmTravelled`

because a variable name is valid as an expression—the resultant value is just
whatever that variable’s value is. But we could use literals, as Example 2-7 shows. (A trap awaits the
unwary here; see the sidebar on the next page.)

Example 2-7. Dividing one literal by another

60 / 10

Or we could use a mixture of literals and variable names to calculate the elapsed time in minutes:

elapsedSeconds / 60

or a multiplication expression as one of the inputs to a division expression to calculate the elapsed time in hours:

elapsedSeconds / (60 * 60)

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