Introduction to Computing Concepts

1. Introduction to Computing Concepts Note Set 7

2. Overview • Variables • Data Types • Basic Arithmetic Expressions • Arithmetic

3. Memory in a computer • Computer uses a few levels of memory to hold data that it is using in processing. RAM 3366 3368 3370 3372 3374 3376

4. Data • Collection of raw facts or figures • Perform some processing on data in order to obtain information • Example Data: Test Grades • Example Information: Class Average, Standard Deviation, etc. • Data (and info.) usually has an intrinsic Data Type • Numerical Data (test grades)? String Data (names)? 3.1415927 Bob, Sam, Jane Computer Science 99

5. Data in Java • Need some way to store data/info while program is running/processing • For this, we use variables • Allow storage a piece of data • Will become “larger” or “smarter” as the semester progresses • Each has a particular data type

6. Data Types • To efficiently use the computer’s memory, each variable has a data type • Behind the scenes, tells the compiler and JVM how to use memory to store a pieces of data • E.g. A number is stored differently than an integer • Java is a Strongly Typed Language • The languages enforces rules as to what you can do with the data in variables • E.g. Won’t necessarily let you do this? “Bob” + 27 Doesn’t necessarily make sense to add a string and number…

7. 2 Categories of Data Types • Primitive Data Types • Holds a single data item such as integer, character, or true/false value • Reference Data Types • Data type whose value is actually a memory address

8. Primitive Data Types

9. Declaring Variables • declaration statement • Line of code that identifies, or declares, the type and names the identifier or variable. General Form: SomeDataTypeSomeIdentifierName; float price; int grade; long atomsInBody; double Average;

10. Declaring Variables – Identifier Names • Rules for names of Identifiers • must start with letter, underscore or dollar sign ($) • subsequent characters can be letters, underscores, dollar signs, or digits (0 – 9) • Any Length (but be reasonable) • Name should be meaningful (no variables named x, y, z) • Remember – Java is Case Sensitive • Can’t declare 2 variables with the same name in the same method • Can’t have a variable that is a reserved word or the same name as a method General Form: SomeDataTypeSomeIdentifierName; Where have we seen these rules before?

11. In Code public class TestVariables { public static void main (String [] args) { int grade1 = 100; int grade2, grade3; float average; //Other stuff here } } Notice that you can declare the variable and provide an initial value all in one statement.

12. check point • Declare a variable to hold your GPA • Declare a variable to hold your age (in years)

13. Assignment Statements • Used to store a new value in a variable • uses the assignment operator (=) userAge = 21; boolean flag newUserAge = userAge; sum = grade1 + grade2 + grade; float average = sum / 3.0;

14. Assignment Statements int grade1 = 98; int grade2 = 100; int sum = grade1 + grade2; • = is right associative • Means always stores what’s on the right side in the variable on the left side • Will evaluate expression on right first (step 1), then perform the assignment Step 2 Stores 198 in sum Step 1 Evaluates to 198

15. Variables in Output • Can use a variable in an output statement • Can concatenate a string literal and variable with plus sign userAge = 21; System.out.println(userAge); System.out.println(“Age is “ + userAge);

16. Important Arithmetic Operators in Java

17. Important Arithmetic Operators in Java Might Be New Math Ideas

18. check point • What is the result of? • 3 / 2 • 2 / 3 • 5 % 4 • 4 % 5

19. Arithmetic Operators • The order of operator precedence is a predetermined order that defines the sequence in which operators are evaluated in an expression • Addition, subtraction, multiplication, and division can manipulate any numeric data type • When Java performs math on mixed data types, the result is always the larger data type • Casts allow programmers to force a conversion from one primitive type to another

20. Numeric Expressions • Any Expression that can be evaluated to a number • Can include operators, literal values, variables, method calls • Only primitive data types may participate in numeric expressions • Any method calls we use in a numeric expression will return a primitive data type. • A literal value and a variable (or 2 variables) must be separated by an arithmetic operator

21. What if multiple operators in 1 expression? • Follow the order of Precedence • Unless parentheses dictate otherwise, evaluate expressions in the following order • Multiplication and/or Division • Integer Division • Modular Division • Addition and/or subtraction • When multiple operations of the same kind are present, Java performs the left to right 18 / 3 – 2 + 4 * 2

22. Let’s Evaluate 18 / 3 – 2 + 4 * 2 6 – 2 + 4 * 2 6 – 2 + 8 4 + 8 12

23. Parentheses in Expressions • Change the order of operations • when found in an expression, the part inside the parentheses is evaluated first. Then the rest of the expression is evalutated • If they are nested, then the inner-most set of parentheses is evaluated first

24. Let’s Evaluate 18 / (3 – 2) + 4 * 2 18 / 1 + 4 * 2 18 + 4 * 2 18 + 8 26

25. check point – Your Turn! 18 / 3 * 2 + (3 * (2 + 5))