Modem

Modem

•Do modulation

•D2A and A2D converter

•Mode+demod=modem

Different Types

Different Types

The many different types of information systems can be divided into categories based on where they are used in the hierarchy of an organization.

What is an Information System?

What is an Information System?

Many organizations work with large amounts of data. Data are basic values or facts and are organized in a database. Many people think of data as synonymous with information; however, information actually consists of data that has been organized to help answers questions and to solve problems. An information system is defined as the software that helps organize and analyze data. So, the purpose of an information system is to turn raw data into useful information that can be used for decision making in an organization.

Typical Components of Information Systems

While information systems may differ in how they are used within an organization, they typically contain the following components:

1. Hardware: Computer-based information systems use computer hardware, such as processors, monitors, keyboard and printers.
2. Software: These are the programs used to organize, process and analyze data.
3. Databases: Information systems work with data, organized into tables and files.
4. Network: Different elements need to be connected to each other, especially if many different people in an organization use the same information system.
5. Procedures: These describe how specific data are processed and analyzed in order to get the answers for which the information system is designed.

The first four components are part of the general information technology (IT) of an organization. Procedures, the fifth component, are very specific to the information needed to answer a specific question.

Structure of C program and Why we put braces () with main

Structure of C program

•A C program consist of following parts.

•1- preprocessor Directive (#include<iostream.h>)

•2-main function                                                 void main ()

•{   

•  program body

• }

Why we put braces () with main

•Braces tells the compiler that the word “main” is name for a function. Otherwise compiler will consider it is name of some variable or identifier.

•If braces are empty it means function do not take input from some other function

•Like void main()

•If braces are not empty then it means function may take input arguments.

•Like void main(int a , char b ) means this funciton can take two input arguments.

Example program and Rules for writing a program

Example program

•#include<stdio.h>

•#include<conio.h>

•void main()

•{

•  printf”Hellow world";

•getch();

•}

•

Rules for writing a program

•All the names of the variables and other words should be in lower case

•The first function of the program should be main.

•All the program should be in medium braces {}

•After each instruction of the program we should put semicolon but no semi colon after main, preprocessor directive and braces because they are a part of program but not executed like other instructions.

Comments in a program and Data types

Comments in a program

•Comments are the lines of the program which are ignored during the program execution.

•When a programmer write a program he adds some comments with it to make the program easy to understand.

•Comments may be single line or multiple line.

•Single line comments are proceeded by //

•Multiple line comments should be within this symbol.

•/*       coments     */

Data types

 •Any type of data that is used in c/c++ program has its type with the help of which compiler can recognize it and can reserve space for it in memory.

•Basically two types of data is used in c/c++

•Variable and constant

Data types used in c program and int

Data types used in c program

1- integer variable Int

2- character variable

Char

3- floating point variables

Float

4- Enumerator

Enum

5- class

Class

6- string

Char []

int

•This data type is used to save integer values

•E.g. 2, 25 ,567 etc.

•C++ compiler use 4 bytes to save int

•In old compilers int was of 2 bytes so its range was -32767 – 32768

•It comes in three values, int, short int, long int

•Length of data depends on compiler, but short int is at least 2 bytes and long int is at least 4 bytes

char and float

char

•It is used to save single character

•Like a x b c t / [ ] = etc

•Character that is assigned should be enclosed in   inverted single commas like  ‘    ’.

float

•Float is used to store fractional values.

•Its size depend on compiler .

•Usually it is 2 byte.

•Fractional part may be small or long. so we use  float(small factional size), double (medium fractional size) and long double (long fractional size) for it.

Enumerator and class

Enumerator

•It is used for user defined data type.

•For example:

•Enum weekday {sun, mon, tues, wed, thurs, fri, sat};

•Weekday currentday=wed;

•By default value of enumerator starts from 0

•But we can assign our own values as well.

class

•This is another user defined data type used for sophisticated data.

•How to write

•Class class_name{

•Private_data;

•Public_data;

•}object;

string and constants

string

•String is combination of characters.

•Syntax:

•Char string_name[]= “value”;

constants

•Constants are values which cannot be changed in the program.

•For example we know that value of pi is 3.14 always.

•So whenever we define pi, we define it as constant so that nobody can change its value even by mistake.

How to declare constants

How to declare constants

•There are two ways to declare a constant value

•1- write the word constant before the name of datatype e.g. const int x or const float pi

•2- declare it before main() function.

•E.g . #define pi = 3.14

VARIABLES

variables

•These are values which can change there value during program.

•It can be int, float, char etc. depending on our need.

•if value of variable is changed, its new value is saved and previous value is removed from memory.

BASIC DIFFERENCE BETWEEN C & C++

Basic difference between c & c++

•Standard I/O library used is stdio.h

•It do not use namespace

•For input we use scanf

•For output we use printf

•It supports object oriented programing

•Standard I/O library used is iostream

•We have to use namespace

•We use cin>>

•We use cout<< for output

•It do not support object oriented programing