Chapter 6Programming Languages (1) Introduction to CS 1st Semester, 2016 Sanghyun Park
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)
Programming Language History • ____________ languages (e.g., 5123) • ____________ languages (e.g., ADDI R1, R2, R3) • ____________ languages (e.g., sum = a + b)
First Generation Language • Machine code • Specific to the machine __________ • _____ to write • Even harder to read
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
ADDI R1,R2,R3 Assembler 5123 Assemblers • Since assembly language is _____ to machine language, _________ can be done automatically
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
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 ___________
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
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
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#
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
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)
Evolution of Programming Paradigms
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.
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
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
Sample Variable Declarations
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
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
Constants • Variables that are not allowed to _____ • Once defined, it can’t be changed later • Why use constants? • More ________ code • _______ to modify code
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
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”
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 “_____________”
Arrays: Heterogeneous • A structure that contains multiple values of different kinds
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;
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;
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)));
Control Statements • Alter order of execution of statements in a program • ______-entry / ______-exit • Most common ones • if-then-else • while • switch • for
If Statement
While Statement
Switch Statement
For Statement
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
