Programming Paradigms Introduction

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 2 Definitions Programming Language notation for specifying programs/computations consists of words, symbols, and rules for writing a program Programming Paradigm programming “technique” way of thinking about programming view of a program

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 3 Programming Paradigms Imperative Programming program as a collection of statements and procedures affecting data (variables) Object-Oriented Programming program as a collection of classes for interacting objects Functional Programming program as a collection of (math) functions Others

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 4 Some Languages by Paradigm Imperative (also called Structured or Procedural) Programming FORTRAN, BASIC, COBOL, Pascal, C Object-Oriented Programming SmallTalk, C++, Java Functional Programming LISP, ML, Haskell

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 5 History of Languages 1950s to 1960s FORTRAN, COBOL, LISP, BASIC 1960s to 1970s (ALGOL-based) Pascal and others 1970s to 1980s Prolog, C, Ada 1980s to 1990s C++, ML, Perl, Java

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 6 Paradigm Change For example, from Procedural to Object- Oriented Programming Arises from problems encountered in one paradigm but addressed in another Case study: from C to C++ Evolution from procedural, to modular, to object- based, to object-oriented programming Stroustrup book section 1.2 (2 nd edition, pp ): required reading material

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 7 Case Study: Stacks Stack last-in, first-out structure operations: push, pop Stacks are used to support some solution push and pop are defined and implemented as functions the solution consists of code that invoke these functions

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 8 Implementing a Stack Stack can be implemented as an array array contains pushed elements an integer refers to top of the stack most common implementation Or as a linked list using pointers and dynamic allocation Other implementations

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 9 Array Implementation in C char Store[MAX]; int top = 0; void push(char x) { if (top < MAX) Store[top++] = x; else printf(“full\n”); } char pop() { if (top > 0) return Store[--top]; else printf(“empty\n”); }...

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 10 Using the Stack void application() { … push(‘x’); … result = pop(); … }

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 11 Procedural Programming Focus is on writing good functions and procedures use the most appropriate implementation and employ correct efficient algorithms Stack example (assume array implementation) one source file Store and top are global variables stack and application functions defined at the same level (file)

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 12 Problems Application can alter implementation details can directly manipulate top and Store from application() integrity of stack not ensured Stack code and application code are not separated

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 13 Encapsulation and Modular Programming Focus is on writing good modules hide implementation details from user provide an interface Stack example stack.h contains prototypes for push, pop stack.c contains stack code, Store and top declared static (local to stack.c) application includes stack.h

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 14 Benefits from Modules Application cannot destroy the integrity of the stack Stack implementation can change without affecting application source Question: what happens if we need more than one stack?

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 15 Multiple Stacks Strategy 1 (use structs) in stack.h, define a stack structure that contains Store and top; push, pop now have an extra parameter that specifies which stack application code defines stack variables Strategy 2 (use handles) implement multiple data structures in stack.c use an integer (the handle) to specify “stack number”

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 16 Modules and Multiple Stacks Disadvantage of strategy 1: implementation (data) is exposed back to original problem on stack integrity Disadvantage of strategy 2: stack module will be unnecessarily complex handle is artificial (what if an arbitrary integer is passed?)

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 17 Abstract Data Types and Object-based Programming Focus is on writing good classes (or types) that define operations on objects of the class class defined like a module (encapsulation enforced) but multiple instances now possible user-defined type Stack example (C++) stack.h and stack.cpp define a stack class

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 18 Object-Oriented Programming Incorporates both encapsulation and inheritance through the class concept Focus is on writing good classes and on code reuse Examples Shape, Circle, and Rectangle in a drawing program Employee, Faculty, Staff in a university personnel system

6/15/2005 Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved. L1: Introduction Slide 19 What’s Next? Survey of languages by paradigm Discussion of language features and language design decisions Related areas: language implementation, translation, syntax, semantics