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Computer Science 1 02A-Primitive Types & Expressions

Computer Science 1 02A-Primitive Types & Expressions. Number Bases. The most commonly used bases for numbers in computer science are: Binary (base 2) Alphabet : 0 1 Example: 1001 2 , 0110 2 , 0 2 , 1 2 Octal (base 8) Alphabet : 0 1 2 4 5 6 7 Example: 7 8 , 0 8 , 460 8

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Computer Science 1 02A-Primitive Types & Expressions

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  1. Computer Science 1 02A-Primitive Types & Expressions CS1s - 02A-Primitive Types & Expressions (v2.00)

  2. Number Bases • The most commonly used bases for numbers in computer science are: • Binary (base 2) Alphabet: 0 1 Example: 10012, 01102, 02, 12 • Octal (base 8) Alphabet: 0 1 2 4 5 6 7 Example: 78, 08, 4608 • Decimal (base 10): Alphabet: 0 1 2 3 4 5 6 7 8 9 Example: 10010, 010, 200410 • Hexadecimal (base 16): Alphabet: 0 1 2 3 4 5 6 7 8 9 A B C D E F Example: 916, 016, ACDC16, DEADBEEF16 CS1s - 02A-Primitive Types & Expressions (v2.00)

  3. Converting Number Bases to Decimal • Consider the number 1810: = 1 * 101 + 8 * 100 = 1810 • Consider the number 100102: = 1 * 24 + 1 * 21 = 1810 • Consider the number 1216: = 1 * 161 + 2 * 160 = 1810 1 8 101 100 1 0 0 1 0 24 23 22 21 20 1 2 161 160 CS1s - 02A-Primitive Types & Expressions (v2.00)

  4. Converting Decimal Numbers to Binary • Consider the number 2710: 20=1, 21=2, 22=4, 23=8, 24=16, 25=32 • Continually subtract the largest possible amount and place a 1 in the appropriate bit field 25 = (0) too large 24 = (1) ok, new value is 27-16=11 23 = (1) ok, new value is 11-8=3 22 = (0) too large 21 = (1) ok, new value is 3-2=1 20 = (1) ok, new value is 1-1=0 • 2710 = 110112 CS1s - 02A-Primitive Types & Expressions (v2.00)

  5. Memory • Memory is the storage medium for a program while executing • Memory is organized as a contiguous array of space • All data and instructions are stored in binary form • i.e. the value 1210 = 11002 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 1 1 0 0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 CS1s - 02A-Primitive Types & Expressions (v2.00)

  6. Memory Units • byte = 8 bits • halfword = 16 bits / 2 bytes • word = 32 bits / 4 bytes / 2 halfwords • long = 64 bits / 8 bytes / 4 halfwords / 2 words bit 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 byte 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 halfword 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 long 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 word 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 CS1s - 02A-Primitive Types & Expressions (v2.00)

  7. Memory • To organize data in memory, three pieces of information are needed • The address (starting location) of the data in memory • The value of the data to be stored/loaded • The size (length) of the data in memory Bit address in hexadecimal 0 1 0 1 0 1 0 1 0x10000000 0 1 0 1 0 1 0 1 0x10000008 0 1 0 1 0 1 0 1 0x10000010 0x10000018 0 1 0 1 1 1 0 0 0 1 0 1 0 1 0 1 0x10000020 0 1 0 1 0 1 0 1 0x10000028 0 1 0 1 0 1 0 1 0x10000030 0 1 0 1 0 1 0 1 0x10000038 CS1s - 02A-Primitive Types & Expressions (v2.00)

  8. Variables • In Java, variables are used to model the memory cells • All variables have the following key attributes: • Name • Type • Value • Address intmyVariable = 12; program memory 0x10000000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 CS1s - 02A-Primitive Types & Expressions (v2.00)

  9. Java Primitive Types CS1s - 02A-Primitive Types & Expressions (v2.00)

  10. Declaring Variables • Variable names are case sensitive • i.e. abc is different than aBC • Variables cannot be named the same as reserved words • i.e. illegal variable names: private, class, if • Variables cannot begin with a digit • i.e. 1foo is illegal • Variables may contain upper or lower case letters, digits, underscores or the dollar sign: myVar1 MyVar2 my_var1 my$var CS1s - 02A-Primitive Types & Expressions (v2.00)

  11. Variable Declaration • Variables are created with a declaration statement using the following syntax: type name; • For example: int age; char middleInitial; float payRate; boolean done; • All variables are initialized with a default value based on type CS1s - 02A-Primitive Types & Expressions (v2.00)

  12. Variable Initialization • A variable can be initialized during a declaration statement using assignment type name = value; • For example: int age = 14; char middleInitial = ‘C’; float payRate = 12.65; boolean done = true; CS1s - 02A-Primitive Types & Expressions (v2.00)

  13. Variable Initialization • A variable may be initialized after a declaration statement using assignment name = value; • For example: int age; // age = 0 age = 14; // age = 14 char middleInitial; // middleInitial = \u0000 middleInitial = ‘C’; // middleInitial = ‘C’ boolean done; // done = false done = true; // done = true CS1s - 02A-Primitive Types & Expressions (v2.00)

  14. Initializations • Some initializations are known prior to run time • i.e. Initialize a counter variable to 0 before counting int count = 0; // sum up the numbers and store in count • Other initializations may not be known until the program is already running • i.e. How old is the person running the program? int age = ???; • In this situation, the program will get the data from the user via • Standard input (i.e. a prompt) • File CS1s - 02A-Primitive Types & Expressions (v2.00)

  15. Variables .java public class Variables { public static void main(String args[]) { // declare variable here } } • In class activity: • Create a file Variables.java with emacs • Use the template above and declare/initialize the following: • An integer named myInt • A float named myFloat • A boolean named myBool with an initial value of true • After declaring, print out the value for myBool using: System.out.println(“myBool = “ + myBool); • Compile and run using: % javac Variables.java % java Variables • What happens if you try to print out the un-initialized variables? CS1s - 02A-Primitive Types & Expressions (v2.00)

  16. Arithmetic Expressions • Here are some basic mathematical operators: • addition: + • subtraction: - • division: / • multiplication: * • modulus: % • assignment: = • For example: 2 + 3 // 5 3 – 2 // 1 4 / 2 // 2 3 * 2 // 6 2 % 5 // 2 x = 4 + 5 // x = 9 CS1s - 02A-Primitive Types & Expressions (v2.00)

  17. Arithmetic Expressions • Operators have precedence – just like in math *, /, % left to right +, - left to right = right to left • For example: 2 + 3 * 6 // 2 + (3 * 6) = 20 6 / 3 – 2 * 2 // (6 / 3) – (2 * 2) = -2 2 * 3 % 10 + 2 // ((2 * 3) % 10) + 2 = 8 • To override precedence, use parentheses: () (2 + 3) * 5 // 25 CS1s - 02A-Primitive Types & Expressions (v2.00)

  18. Arithmetic Expressions • Which of the following expressions are valid? • x + y = z; • distance = rate X time; • percent = 10 %; • temp = temp + 1; • temp++; • x = y = z; • x = (1 + (2 + 3); CS1s - 02A-Primitive Types & Expressions (v2.00)

  19. Discuss narrowing of types: • float->double • int->byte • Also discuss mixed mode arithmetic expressions • 1 / 2 • 1. / 2 • (float) 1 / 2, etc… CS1s - 02A-Primitive Types & Expressions (v2.00)

  20. Scanner Class • Scanner is a Java class which supports reading of values from text. (A number is different from a string of characters!) import java.util.Scanner; public class SimpleAge { public static void main (String args[]) { Scanner sc = new Scanner(System.in); System.out.print( "What is your age? " ); int age = sc.nextInt(); System.out.println("You're " + age + " years old."); } } • The class name is Scanner,and the method called within the class is nextInt • Nothing is passed to the method: () • An int is returned from the method CS1s - 02A-Primitive Types & Expressions (v2.00)

  21. Average.java • Navigate to the Scanner page: • CS1S->Java Documentation->Scanner • In class activity: • Create a class, Average, which does the following: • Prompt the user for three integers using the Scanner class • Calculate the average of the three integers • Print the result to standard output • Verify your program works with the following sets of values: 1 2 3 1 3 6 0 0 0 -1 –2 –3 • Sample output: 1 3 6 Result = 3.33333333 CS1s - 02A-Primitive Types & Expressions (v2.00)

  22. Boolean Operators • Booleans are binary values of either true or false • The operators used in boolean expressions and: && or: || xor: ^ not: ! • The truth tables: and or xor not 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 1 0 1 1 1 0 1 0 0 1 0 1 1 0 1 1 1 1 1 1 1 1 1 0 CS1s - 02A-Primitive Types & Expressions (v2.00)

  23. Boolean Operators • What are the results of the following boolean expressions? • true == true • true && false • true && true • true || false • false || false • true ^ true // bitwise exclusive OR • false ^ true • !true CS1s - 02A-Primitive Types & Expressions (v2.00)

  24. Comparison Operators • An expression with integer values can be evaluated to a boolean using comparison operators: less than: < less than or equal: <= equal: == not equal: != greater than: > greater than or equal: >= • For example: 1 < 2 // true 1 <= 1 // true 2 == 3 // false 1 != 2 // true 1 > 2 // false 2 >= 1 // true CS1s - 02A-Primitive Types & Expressions (v2.00)

  25. Operator Precedence • The comparison operators have higher precedence than the boolean operators true == true && 1 < 2 // (true == true) && (1 < 2) • The precedence for the operators we’ve discussed: high precedence low precedence CS1s - 02A-Primitive Types & Expressions (v2.00)

  26. Operator Precedence • Which of the following expressions are valid? For those which are valid, what is the result? • boolean flag = 1 == 2; • boolean flag = 1 != 2 < 10; • boolean flag2 = 1 == 1 && true; • boolean flag = 1 < 2 < 32; • 3 + 5 == 10 – 2 • true || false && false || true • boolean flag = true ^ false && 1 < 2 CS1s - 02A-Primitive Types & Expressions (v2.00)

  27. Temperature Conversion Program • A temperature in degrees Celsius can be converted to Farenheit • Multiply the degrees Celsius by 1.8 and add 32 to get the degrees Farenheit • i.e. 10 degrees Celsius = 50 degrees Farenheit • Write a complete Java program that performs this calculation • First answer the following questions: • What problem are you trying to solve? • What are the inputs and outputs? • How will you verify whether your program is correct? CS1s - 02A-Primitive Types & Expressions (v2.00)

  28. Temperature.java • In class activity: • Create a class, Temperature, which converts a temperature in degrees Celsius to degrees Farenheit • Sample output: Celsius: 13 Farenheit = 55.4 Celsius: 13.2 Farenheit = 55.76 CS1s - 02A-Primitive Types & Expressions (v2.00)

  29. Constants • A constant in Java is like a variable which cannot change value after declaration/initialization • The variable declaration is preceded by the final keyword final double CELSIUS_MUL = 1.8; final double CELSIUS_ADD = 32; • All capital letters (and underscores) are commonly used to indicate a constant • A modification to the Temperature program could be: double farenheit = celsius * CELSIUS_MUL + CELSIUS_ADD; CS1s - 02A-Primitive Types & Expressions (v2.00)

  30. Rectangle.java • In class activity: • Write a complete program, Rectangle.java, that prompts for the length and width of a rectangle, then calculates and prints the perimeter and the area • If you don’t remember the equations, look them up on the web • Be sure to answer the following questions first: • What problem are you trying to solve? • What are the inputs and outputs? • How will you verify whether your program is correct? CS1s - 02A-Primitive Types & Expressions (v2.00)

  31. Circle.java • In class activity: • Write a complete Java program that prompts for the diameter of a circle, then calculates and prints the perimeter and the area • Be sure to answer the following questions first: • What problem are you trying to solve? • What are the inputs and outputs? • How will you verify whether your program is correct? • Look at the methods and constants in the Math class Javadocs: • CS1S->Java API->Math CS1s - 02A-Primitive Types & Expressions (v2.00)

  32. SalesTax.java • In class activity: • Review the source code for SalesTax.java and answer the questions that follow. • http://www.cs.rit.edu/~cs1s/week2/SalesTax.java • Questions: • There is one logic error, can you find it? • The is one style violation, can you find it? • What would happen to this program if the sales tax in this area changed? • Explain one way to make this program more maintainable CS1s - 02A-Primitive Types & Expressions (v2.00)

  33. Revision History • Revision History • v1.00, 9/13/2004 1:22 PM, sps Initial revision. -- v2.00, 9/10/2005, chr CS1s - 02A-Primitive Types & Expressions (v2.00)

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