programming languages

Introduction

•What is a Computer?

Up until the late 1940’s, a Computer was a person who performed calculations

What about now?

•Programs

Programs are sequence of step by step instructions to the computer

Programs, and the data values processed by programs, are called software.

Programming languages

•Low-Level Programming Languages

Machine language

Assembly language


•High-Level Programming Languages
Instructions look more like English and Math
Generally result in multiple low level commands, for a single high level statement.

Machine Language

Used by early computers

Executable by machines, almost incomprehensible to humans

Programming in machine language is very tedious and prone to errors

•Ex

11001010000100101000010101110100

11000101010001110010101000110010

Assembly Language

Mnemonics used for instruction codes

and memory locations

Not directly understandable by

machine. They must be translated

Easier for humans to use and still in

use today.

Ex:

ADD X, Y, Reg1

ADD Reg1, Z, Reg2

STORE Reg2 SUM

High Level Programming Language

•Uses syntax resembling combination of mathematical notation and English

•Easy for humans to understand.

•Not understandable by machines, must be translated using a compiler or an interpreter.

•Programming tools such as integrated programming environment with a debugger are available to aid in

 programming process.

High Level Programming Languages

•Pascal  RESULT := X + Y+ Z;

•FORTRAN  RESULT = X + Y + Z

•COBOL  COMPUTE RESULT = X + Y + Z.

•C  RESULT = X + Y + Z;

•C++  RESULT = X + Y + Z;

•Ada  RESULT := X + Y + Z;

•PL/1  RESULT = X + Y + Z;


Programming Language Translation
•Assemblers
•Interpreters
•Compilers


•Assemblers
–Translate statement from assembly language to machine language
–Generally use table look-up techniques
•Interpreters
–Translate and execute each high-level statement, one at a time

•

–Translate the entire high level language program, called the source code, to machine language and store the
  result.

–Machine language code produced by compilers is called object code


Programming Paradigms 
•Object-Oriented Paradigm


System Software
•Operating System

  –Memory and resource management

  –Job scheduling

  –Security

•Command Line vs. Graphical User Interface

  –Note: the vi editor

Problem Solving and Software Development

•Development and Design

–Analyze the problem

–Develop a solution

–Code the solution

–Test and debug


•Documentation


–Internal documentation


•Comments – Notes to the reader of the program


•Identifiers – should represent the information they hold or the task they define.


–External documentation

•User’s manual

•Test plan

•Design document



•Maintenance

–Correcting new problems

–Adding new features

–Modifications due to change in requirements

Algorithms
•An Algorithm is a step by step sequence of instructions.
–It must be unambiguous
–It must be doable
–Each step must terminate, and the entire algorithm must terminate

•Expressions of Algorithms are
–Pseudocode
–Flowcharts

Example of Algorithm 
•Write an algorithm that will determine the largest value of four values.  

A flowchart solution
•INPUT first value, STORE value in Largest.

•Loop to determine if any other numbers are larger.
 DISPLAY Largest

A pseudocode solution
•INPUT first value, STORE value in Largest

•Repeat three times

•INPUT next value, store in Number

•IF Number >Largest,

•STORE Number in Largest

•DISPLAY largest

Control Structures
•Sequence

–Execute sequence of statements in order given.

–This is the default control structure.

•Selection

–Select between alternative paths.

•Iteration

–Repeat a statement or collection of statements over and over again.

•Invocation

–Execute a complex task, which is written separately