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Variables can be given any value that matches their type.
The Java statement that gives a variable its value
is called an assignment statement.
After a variable is given a value, the variable is
said to be initialized.
These aren’t equations! Read “=” as “gets” deposit = 4; my_num = 3.4; name = “CSC 130”;

 You can use the assignment operator (=) and math operators (*,/,+,-) to do arithmetic.
 Remember your order of operations! (PEMDAS)
 The thing on the left gets changed.
 value = 4+3*10;
 interest = 3.0/2.0;
 due = value+interest;
The right-hand sides are expressions , just like in math.

 The following table summarizes the arithmetic operators available in Java.
This is an integer division where the fractional part is truncated.

 We can change the value of a variable. If we want the value to remain the same, we use a constant .
final double PI = 3.14159; final int MONTH_IN_YEAR = 12; final short FARADAY_CONSTANT = 23060;
The reserved word final is used to declare constants.
These are constants, also called named constant
.
These are called literal constant.

 Block of code: Denoted by { }
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Scope: The area of code in which a variable is available for use
A variable’s scope is the block in which it is declared

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You must declare and initialize a variable before using it on the right of a rule.
Only the variable to the left of the = gets changed
There can be one and only one variable on the left.
You cannot put data into a variable that does not match the variables’ type.
You can only have one variable with any given name in a particular block.

 Assignment statements are NOT math equations!
 count = count + 1;
 These are commands!
 value = 2;
 interest = value;
 value = value + 3;
 What’s the value of interest?

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 There’s no such thing as: z
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3 x
4( y
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12)

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Double Division: no rounding
 3.0 / 6.0
 6.0 / 3.0
 x/1.5
 At least one number must have a decimal
 Integer Division: round DOWN
 3/6
 6/3
 x/y, if both x and y are ints
 Both numbers are integers

 int x = 6/4;
 int y = 4/6;
 double z = 4/6;
 double a = 6/4;
 double b = 6/12.0;
 int c = 6.0/12;

 Modular Arithmetic: Remainder from division
 Works with integers only
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Operator is % (NOT PERCENT!)
6 % 4 is read “six mod four”
 3 % 6 =
 7 % 2 =
 7 % 14 =
 14 % 7 =

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What useful thing does % 10 do?
 3 % 10 =
 51 % 10 =
 40 % 10 =
 678 % 10 =
What useful thing does /10 do (integer division?)
 3/10 =
 51/10 =
 40/10=
 678/10 =
What useful thing does % 2 do?

 To change a variable’s type, you can cast from one type to another
 int x = 4;
 double y = 10/(double)x;
 This is illegal:
 int x = 5.5;
 This is legal:
 int x = (int)5.5;

 Increment Operator
 x =x + 1;
 x++;
 Decrement Operator
 x = x – 1;
 x--;
 And others:
 x += 2;
 amount *= 1.05;

 Random numbers – generate with the
Math object.
 Random double between x and y: double rand = Math.random()*(y-x)+x;
 Random int between x and y (inclusive): int rand = (int)(Math.random()*(y-x+1)+x);
Be careful with parentheses!

 You can print to the console window:
 System.out.println(“Hello!”);
 String word = “Hey”;
 System.out.println(word);
 System.out.println(45+5);
 int y = 45+5;
 System.out.println(y);
 System.out.println(“y”);
 System.out.println(“The answer is “+y);
 System.out.print(“Stay on this line “);
 System.out.print(“and keep printing.”);

 Average three numbers
 Fahrenheit to Celsius
 C = (5/9)(F-32)
 Given a big number, (> 1000), print its last three digits in reverse order (Ex: if input is
1234, prints out 432)