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COMP 14 Introduction to Programming

COMP 14 Introduction to Programming. Miguel A. Otaduy May 13, 2004. Review Exercise. Execution of c=2*a+b in a computer. Today in COMP 14. Java special symbols identifiers data types operators expressions Strings. Reading Check-Up. syntax.

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COMP 14 Introduction to Programming

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  1. COMP 14Introduction to Programming Miguel A. Otaduy May 13, 2004

  2. Review Exercise • Execution of c=2*a+b in a computer

  3. Today in COMP 14 • Java • special symbols • identifiers • data types • operators • expressions • Strings

  4. Reading Check-Up syntax • The rules of a language determine which instructions are valid. • True or False? Hello! is an example of a legal Java identifier. • If an operator has an integer and a floating-point operand, the result of the operation is a number. • The expression (int) (9.2) evaluates to False floating-point 9

  5. Introduction • Computer program: a sequence of statements whose objective is to accomplish a task • Programming:process of planning and creating a program • Programming language: a set of rules, symbols, and special words

  6. Sample Java Program public class Hello { public static void main (String[] args) { System.out.println ("Hi There!"); } } Upon execution, this program would display Hi There!

  7. Programming Languages • Programming languages have rules of grammar just as English does • syntax rules - which statements are legal and which are not • semantic rules - determine the meaning of the instructions • token - smallest individual unit of a program • special symbols • word symbols • identifiers

  8. Special Symbols + - * / . ; ? , <= != == >=

  9. int float double char void public static throws return Word Symbolsaka reserved words, or keywords • reserved words are always all lowercase • each word symbol is considered to be a single symbol • cannot be used for anything other than their intended • purpose in a program • shown in blue typewriter font in textbook • full table in Appendix A

  10. Identifiers • Names of things (variables, constants, methods) in your programs • Can be composed of any combination of letters, digits, underscore (_), and dollar sign ($) • Cannot begin with a digit • May be any length • Java is case-sensitive • Total, total, and TOTAL are different identifiers

  11. Illegal Identifiers

  12. Questions Classify the following as legal or illegal identifiers: • My First Program • my1stProgram • 1stProgram • $money • an_identifier • Jane'sProgram illegal legal illegal legal legal illegal

  13. Primitive Data TypesWhat’s A Data Type? • A set of values and the operations that can be performed on those values • Primitive data are fundamental values such as numbers and characters • Operations are performed on primitive types using built-in operators

  14. Primitive Data Types • 8 primitive data types in Java • 4 represent integers • byte, short, int, long • 2 represent floating point numbers • float, double • 1 represents characters • char • 1 represents boolean values • boolean

  15. Primitive Data TypesNumeric Types • The difference between the various numeric primitive types is their size, and therefore the values they can store: Type byte short int long float double Storage 8 bits 16 bits 32 bits 64 bits 32 bits 64 bits Min Value -128 -32,768 -2,147,483,648 < -9 x 1018 +/- 3.4 x 1038 with 7 significant digits +/- 1.7 x 10308 with 15 significant digits Max Value 127 32,767 2,147,483,647 > 9 x 1018

  16. Integers • Examples: -6728, -67, 0, 78, 36782 • Positive integers do not have a '+' sign in front of them (but they can) • No commas are used in an integer • commas in Java are used to separate items in a list

  17. Primitive Data TypesCharacters • A char stores a single character from the Unicode character set • an ordered list of characters, and each character corresponds to a unique number • uses 16 bits per character, allowing for 65,536 unique characters • Character literals are delimited by single quotes: 'a' 'X' '7' ' ' '$' ',' '\n' newline character (we'll discuss later)

  18. Primitive Data TypesBooleans • Only two valid values • true or false • uses 1 bit for storage • Represent any situation that has 2 states • on - off • true - false • true and false are reserved words

  19. Arithmetic Expressions • Expression - a combination of one or more operands and their operators • Arithmetic expressions compute numeric results and make use of the arithmetic operators: • If either or both operands associated with an arithmetic operator are floating point, the result is a floating point Addition + Subtraction - Multiplication * Division / Remainder %

  20. Division and Remainder • If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded) • The remainder, or modulus, operator (%) returns the remainder after dividing the second operand into the first (only works with integer types) 14 / 3equals? 4 8 / 12equals? 0 14 % 3equals? 2 8 % 12equals? 8

  21. Unary vs. Binary Operators • Unary operators • has only one operand • example: - (negative, not subtraction) -5 • Binary operators • has two operands • example: - (subtraction) 5 - 3

  22. Operator Precedence • Determines the order in which operators are evaluated: • multiplication, division, and remainder • addition, subtraction, and string concatenation • arithmetic operators with the same precedence are evaluated from left to right • Parentheses can be used to force the evaluation order (just like in math)

  23. Operator Precedence • What is the order of evaluation in the following expressions? a + b + c + d + e a + b * c - d / e 1 2 3 4 3 1 4 2 a / (b + c) - d % e 2 1 4 3 a / (b * (c + (d - e))) 4 3 2 1

  24. Integral Expressions • All operands are integers • Result is an integer • Examples: 2 + 3 * 5 3 + x – y / 7 x + 2 * (y – z) + 18

  25. Floating-point Expressions • All operands are floating-point numbers • Result is a floating-point • Examples: 12.8 * 17.5 – 34.50 x * 10.5 + y - 16.2 7.0 / 3.5

  26. Mixed Expressions • Operands of different types • Examples: 2 + 3.5 6 / 4 + 3.9 • Integer operands yield an integer result • Floating-point operands yield a floating-point result • If both types of operands are present, the result is a floating-point number • implicit type coercion • Precedence rules are followed 2.0 + 3.5 1 + 3.9 1.0 + 3.9

  27. Type Conversion (Casting) • Used to avoid implicit type coercion • Syntax (dataTypeName) expression • Expression evaluated first, then type converted to dataTypeName • Examples: (int) (7.9 + 6.7) = 14 (int) (7.9) + (int)(6.7) = 13

  28. QuestionsEvaluate These Expressions 9 % 6 3 • (5 + 4) % 6 • (5 + 6) % 3.5 • (double) (13) / 2 • (double) (13 / 2) 11 % 3.5 not possible 13.0 / 2 6.5 (double) (6) 6.0

  29. The class String • String • sequence of zero or more characters • enclosed in double quotation marks • null or empty strings have no characters • numeric strings consist of integers or decimal numbers • length is the number of characters in a string • The class String is used to manipulate strings • Examples: • "Hello World" • "1234" • "45.67" • ""

  30. Strings • Every character has a position in the string (starting with 0) "Hello World" • The length of the string is the number of characters in it • what's the length of "Hello World"? 0123456789... 11 (count the space)

  31. Parsing Numeric Strings • In Java, input from the user comes in the form of a string • we need to know how to get the number values out of the string • Numeric String • a string with only integers or decimal numbers • "6723", "-823", "345.76"

  32. Parsing Numeric Strings • String to int Integer.parseInt(strExpression) Integer.parseInt("6723") 6723 • String to float Float.parseFloat(strExpression) Float.parseFloat("345.76") 345.76 • String to double Double.parseDouble(strExpression) Double.parseDouble("1234.56") 1234.56

  33. Summary • Identifiers • can be composed of any combination of letters, digits, underscore (_), and dollar sign ($) • cannot begin with a digit • Java is case-sensitive • Data Types • main integer type: int • main floating-point type: double • others: char, boolean

  34. Summary • Arithmetic Operators: • If one of the operands is floating-point, the result is a floating-point • Can only use % with two integer operands • Casting • (int) (54.9)- truncates the floating-point number • (double) (23) - adds a .0 to the integer addition + subtraction - multiplication * division / remainder (mod) %

  35. To do • Homework 1 due tonight • Homework 2 due tomorrow night • Algorithm design • Theory questions • First program (after tomorrow’s class) • Read ch. 2 (pp. 37-end)

  36. Tomorrow • First QUIZ! • Writing a whole program

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