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
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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
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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 (2nd edition, pp. 14-22):
required reading material

6/15/2005
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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(“fulln”);
}
char pop()
{
if (top > 0)
return Store[--top];
else
printf(“emptyn”);
}
...

6/15/2005
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Manila University. All rights reserved.
L1: Introduction
Slide 10
Using the Stack
void application()
{
…
push(‘x’);
…
result = pop();
…
}

6/15/2005
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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
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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
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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
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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
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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
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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
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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