Chapter 6 Programming Languages (1)

1. Chapter 6Programming Languages (1) Introduction to CS 1st Semester, 2016 Sanghyun Park

2. Outline • Historical Perspective • Traditional Programming Concepts • Procedural Units (next file) • Language Implementation (next file) • Object-Oriented Programming (skip) • Programming Concurrent Activities (skip) • Declarative Programming (skip)

3. Programming Language History • ____________ languages (e.g., 5123) • ____________ languages (e.g., ADDI R1, R2, R3) • ____________ languages (e.g., sum = a + b)

4. First Generation Language • Machine code • Specific to the machine __________ • _____ to write • Even harder to read

5. Second Generation Language • Assembly language • Usually a 1-1 _________ to machine code,e.g., ADDI R1, R2, R3 instead of 5123 • ______ to read and write • Still specific to the machine architecture • Better, but not by much

6. ADDI R1,R2,R3 Assembler 5123 Assemblers • Since assembly language is _____ to machine language, _________ can be done automatically

7. Third Generation Languages • High level, machine ___________ • Much easier to read and write,e.g., money = bills + coins instead of ADDI R1, R2, R3 • Fortran and ______ are early examples

8. 1101 1202 5312 3300 A = B * C Compiler Compilers and Interpreters • High-level code needs to be translated into machine language • Compilers do so _______ of time • Interpreters do so ___________

9. Programming Paradigms • Languages can be classified by ________ • Many different programming languages • Only a few programming paradigms • Imperative/Procedural programming • Object-oriented programming • Functional programming • Logic/Declarative programming

10. Imperative Programming • Traditionally the most _________ • The approach we have seen so far • Program is a _______ of steps • Receives input • Executes a sequence of commands for some computation • Generates output • Examples: Fortran, C, COBOL, Pascal

11. Object-Oriented Programming • Program is a collection of ________ • An object contains __________ describinghow that object should respond to various ________(icon object and list object, for example) • Interaction between objects is via __________ passing • Examples: Smalltalk, C++, Java, C#

12. Functional Programming • This paradigm views the process of program development as connecting predefined “______ ______”, each of which accepts inputs and produces outputs Lisp Expression:(Divide (Sum Numbers) (Count Numbers)) Example: Lisp, Scheme, ML

13. Logic/Declarative Programming • Describe the _________ not the solution • The idea here is to discover and implement a ________ problem-solving algorithm • Once this is done, problems can be solved by developing a precise _________ of the problem • A major obstacle is the discovery of the underlying problem-solving algorithm • For this reason early declarative languages were designed for use in _________ applications • More recently, formal logic within ____________ gave a tremendous boost to this paradigm; this resulted in the emergence of logic programming (e.g., Prolog)

14. Evolution of Programming Paradigms

15. Traditional Programming Concepts • We consider some of the concepts found in imperative and object-oriented programming languages • We will draw examples from the languagesC, C++, C#, Fortran, Java and Pascal • Appendix D contains a brief background of each lang.

16. Variables • Hold a temporary value that can _______ • Some languages insist that a variable should have a ______, while others do not • Example: Java • To store an integer, use an int • To store a real number, use a float • To store a string, use a String

17. Data Types • Common • integer for ______ numbers (16 or 32 bits) • float for ______ numbers (32 or 64 bits) • character for data consisting of _________(ASCII (8 bits) or Unicode(16 bits)) • Sometimes available • Boolean for 0 or 1 (1 bit) • String for string of characters (variable length) • Many others

18. Sample Variable Declarations

19. Literals • Value is explicitly stated in a program • int X = 10 (10 is a literal) • String Name = “Bob” (“Bob” is a literal) • Wage = hours  9.00 (9.00 is a literal) • Although sometimes necessary,the use of literals should be _______ wherever possible

20. Literals: Problem • Example • AverageSales = Sales / 10 • AverageSalary = Salary / 10 • Pay = Hours  10 • What does 10 mean in each of the previous examples? • Literals can ______ the meaning of the statementsin which they appear • Literals can complicate the task of ________ the program • _________ should be used wherever possible

21. Constants • Variables that are not allowed to _____ • Once defined, it can’t be changed later • Why use constants? • More ________ code • _______ to modify code

22. Data Structures • A way of thinking _________ data itemsas ______ larger data item • Different operations can be performedon different data structures • ________ is the most basic example • We will see others later

23. Arrays: Homogeneous • A structure that contains multiple values of the ______ kind • An array of integers • A string can be thought of as an array of _________“This is a string”

24. Arrays: Homogeneous Example • In C, C++, Javachar B[20] = “This is a string”; • You can access any item in an array • Index starts at __, not at __ • For instance, if we execute B[2] = ‘u’,the array above will become “_____________”

25. Arrays: Heterogeneous • A structure that contains multiple values of different kinds

26. Assignment Statements • Assign to a variable • Value of another variable • Result of a computation • Result from a function • C, C++, Java • Total = Price + Tax; • Pascal • Total := Price + Tax;

27. Assignment Example • What are A and B at the end of the following?int A, B;A = 2;B = 3;A = A+A;A = A+B;B = B  B;

28. Operator Precedence • What is A at the end of the following?int A=2, B=3;A = A / B + B * A – A + B; • Most programming languages will doA = (A / B) + (B * A) – A + B; • Use ___________ to override precedenceA = A /( (B + B) * (A – (A + B)));

29. Control Statements • Alter order of execution of statements in a program • ______-entry / ______-exit • Most common ones • if-then-else • while • switch • for

30. If Statement

31. While Statement

32. Switch Statement

33. For Statement

34. Comments • ____________ statements within the code • Should not just repeat the code, but __________ on it • ________ by compiler • C, C++, Java /* Insert Comments here */ // Or put them here