1. Programming Languages and Paradigms
Introduction

2. Definitions Programming Language Programming Paradigm
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
4/18/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

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
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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
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5. History of Languages 1950s to 1960s 1960s to 1970s 1970s to 1980s
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
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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 ): required reading material
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7. Case Study: Stacks Stack Stacks are used to support some solution
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
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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
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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”); }
...
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10. Using the Stack void application() { … push(‘x’); result = pop(); }
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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)
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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
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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
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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?
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15. Multiple Stacks Strategy 1 (use structs) Strategy 2 (use handles)
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”
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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?)
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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
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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
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19. What’s Next? Survey of languages by paradigm
Discussion of language features and language design decisions
Related areas: language implementation, translation, syntax, semantics
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