CSC 241 Lecture, Fall 2012

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Computer Science: An Overview Tenth Edition by J. Glenn Brookshear Chapter 6: Programming Languages 6-2 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 6: Programming Languages • 6.1 Historical Perspective • 6.2 Traditional Programming Concepts • 6.3 Procedural Units • 6.4 Language Implementation • 6.5 Object Oriented Programming • 6.6 Programming Concurrent Activities • 6.7 Declarative Programming 6-3 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.1 Generations of programming languages 6-4 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Second-generation: Assembly language • A mnemonic system for representing machine instructions – Mnemonic names for op-codes – Identifiers: Descriptive names for memory locations, chosen by the programmer 6-5 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Assembly Language Characteristics • One-to-one correspondence between machine instructions and assembly instructions – Programmer must think like the machine • Inherently machine-dependent • Converted to machine language by a program called an assembler 6-6 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Program Example Machine language 156C 166D 5056 30CE C000 Assembly language LD R5, Price LD R6, ShippingCharge ADDI R0, R5 R6 ST R0, TotalCost HLT 6-7 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Third Generation Language • Uses high-level primitives – Similar to our pseudocode in Chapter 5 • Machine independent (mostly) • Examples: FORTRAN, COBOL • Each primitive corresponds to a sequence of machine language instructions • Converted to machine language by a program called a compiler 6-8 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.2 The evolution of programming paradigms 6-9 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.3 A function for checkbook balancing constructed from simpler functions 6-10 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.4 The composition of a typical imperative program or program unit 6-11 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Data Types • Integer: Whole numbers • Real (float): Numbers with fractions • Character: Symbols • Boolean: True/false 6-12 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Variable Declarations float Length, Width; int Price, Total, Tax; char Symbol; 6-13 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.5 A two-dimensional array with two rows and nine columns 6-14 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.6 The conceptual structure of the heterogeneous array Employee 6-15 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.7 The for loop structure and its representation in C++, C#, and Java 6-16 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Procedural Units • Local versus Global Variables • Formal versus Actual Parameters • Passing parameters by value versus reference • Procedures versus Functions 6-17 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.8 The flow of control involving a procedure 6-18 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.9 The procedure ProjectPopulation written in the programming language C Figure 6.10 Executing the procedure Demo and passing parameters by value Figure 6.11 Executing the procedure Demo and passing parameters by reference 6-21 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.12 The function CylinderVolume written in the programming language C 6-22 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.13 The translation process 6-23 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.14 A syntax diagram of our if-then-else pseudocode statement 6-24 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.15 Syntax diagrams describing the structure of a simple algebraic expression 6-25 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.16 The parse tree for the string x + y x z based on the syntax diagrams in Figure 6.17 Figure 6.17 Two distinct parse trees for the statement if B1 then if B2 then S1 else S2 6-27 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.18 An object-oriented approach to the translation process 6-28 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Objects and Classes • Object: Active program unit containing both data and procedures • Class: A template from which objects are constructed An object is called an instance of the class. 6-29 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.19 The structure of a class describing a laser weapon in a computer game 6-30 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Components of an Object • Instance Variable: Variable within an object – Holds information within the object • Method: Procedure within an object – Describes the actions that the object can perform • Constructor: Special method used to initialize a new object when it is first constructed 6-31 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.21 A class with a constructor 6-32 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Object Integrity • Encapsulation: A way of restricting access to the internal components of an object – Private versus public 6-33 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.22 Our LaserClass definition using encapsulation as it would appear in a Java or C# program 6-34 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Additional Object-oriented Concepts • Inheritance: Allows new classes to be defined in terms of previously defined classes • Polymorphism: Allows method calls to be interpreted by the object that receives the call 6-35 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Programming Concurrent Activities • Parallel (or concurrent) processing: simultaneous execution of multiple processes – True concurrent processing requires multiple CPUs – Can be simulated using time-sharing with a single CPU 6-36 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.23 Spawning threads 6-37 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Controlling Access to Data • Mutual Exclusion: A method for ensuring that data can be accessed by only one process at a time • Monitor: A data item augmented with the ability to control access to itself 6-38 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Declarative Programming • Resolution: Combining two or more statements to produce a new statement (that is a logical consequence of the originals). – Example: (P OR Q) AND (R OR Q) resolves to (P OR R) – Resolvent: A new statement deduced by resolution – Clause form: A statement whose elementary components are connected by the Boolean operation OR • Unification: Assigning a value to a variable so that two statements become “compatible.” 6-39 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.24 Resolving the statements (P OR Q) and (R OR ¬Q) to produce (P OR R) 6-40 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Figure 6.25 Resolving the statements (P OR Q), (R OR ¬Q), ¬R, and ¬P 6-41 Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Prolog • Fact: A Prolog statement establishing a fact – Consists of a single predicate – Form: predicateName(arguments). • Example: parent(bill, mary). • Rule: A Prolog statement establishing a general rule – Form: conclusion :- premise. • :- means “if” – Example: wise(X) :- old(X). – Example: faster(X,Z) :- faster(X,Y), faster(Y,Z).