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Java TOPIC 07 – ARITHMETIC
EXPRESSIONS
LESSON NOTE
ASSIGNMENT STATEMENTS We have seen that if we want to store a value in a variable, we
can use a statement such as the following: x = 8; The statement above of course requires that the variable x
already be declared. Statements such as above that assign a value to a variable are
called assignment statements. It is important that both sides of the statement be of the same
type. More on this later. GENERAL FORM In general, assignment statements have the following form: varName = value; LITERALS & TYPES The numbers as they appear in assignment statements are what is
called literals. It is important to note that these literals
have a type. The number 7 will be
an integer while the number 8.3
will be a double. If you want the
number 7 to be taken as a double,
then you need to put 7.0. COMMON ERROR –
UNMATCHING TYPES A common error is to try to store a double value inside of an
integer. int c = 7.5; //will cause an error The opposite does not cause an error as
Java does a built-in conversion. double b = 7; //no error, Java converts 7 to 7.0
An arithmetic expression
is simply an expression consisting of one or more arithmetic operations. The value
part of an assignment statement can be an arithmetic expression that the
computer will calculate into a value. EXAMPLES OF SIMPLE
ARITHMETIC EXPRESSIONS Here are examples of assignment statements containing arithmetic
expressions: totalMinutes = 72
+ 70 + 71 + 70; difference =
109 – 71; q = 9 / 7; MAY CONTAIN VARIABLES Arithmetic expressions can contain numbers, operators and
variables. Note that variables inside
the expression must be initialized (must have a value).
Here is a program that shows arithmetic expressions that contain
previously initialized variables. double diameter = 12.5 double radius =
diameter / 2; double circumference =
2 * 3.14 * radius; double area = 3.14 *
radius * radius; Note that for the program above to do anything of value, we
would have to output to screen the variables of interest. COMMON ARITHMETIC
OPERATORS Here
are the common arithmetic operators used in Java. Of note, we use the asterisk to denote
multiplication. We also use the slash
to denote division.
BEDMAS The
order of which all operations inside an arithmetic expression follows BEDMAS.
The % operator has the same precedence as multiplication and division. To
use brackets, you use the following symbols:
( ) BEDMAS EXAMPLES In each example below, try to figure out what value the variable
answer will get. a) x = 3 + 4 * 2; b) x = 2 * 5 + 14 / 2; c) x = 2 + 10 / 2 The solutions are 11, 17 and 7. INTEGER DIVISION When we do a division, if the two numbers involved
are integers, the result will also be an integer. Therefore, 11 / 2 is 5 while
11.0/2.0 is 5.5.
TYPE CASTING We
saw earlier that we cannot give a double value to an integer variable. This would lead to an error. If
we ever need to convert a double value to an int value, we can use type casting to do so. Type casting
simply means to force the conversion of data from one type to another. To
type cast from double to int, we use the following: double d =
2.93; int x = (int)d; The
(int) automatically converts the
value of d to an integer. However, it is important to understand that the
decimal places are simply removed (truncated). There is no rounding that
takes place. In the code above, x would get 2. VARIABLES
ON BOTH SIDES OF ASSIGNMENT STATEMENTS An assignment statement can have the
same variable appear on both sides of the assignment statement. Simply remember that the right hand
side is calculated by the computer without any consideration for the left
hand side. Once an answer is
calculated, it is stored in the variable that appears on the left hand side. Here are some examples: Example 1 – Increasing a variable’s
value by one count
= count + 1; Example 2 – Decreasing a variable’s
value by one counter
= counter - 1; Example 3 – Doubling a variable’s
value num
= num * 2; Example 4 – Squaring a variable’s
value x
= x * x;
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