cpp-study notes

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Ashfaq Ahmed Waraich

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LanguagesA programming language is a means for you, to generate those

instructions so that the computer can manipulate the data in the

way you want it manipulated.

Computer is such a device that manipulates numbers. Some of the

numbers are interpreted as instructions by the computer while

some as data.

Types Of Languages.

(1). Low Level Languages.

(2). High Level Languages.

(1)-Low Level Languages.

The languages, which are close to machine language,computer's own language, are called low level languages and these

languages are far from human languages like English.

Advantages.

Programmes are highly efficient. Programmes require minimum time to run. Minimum instructions are required.Disadvantages Programmes are difficult to read and write. Programmes are not portable, i.e. a programme written on a

computer will not run on another computer. Everytime a

programme will be written on every new computer.

Languages are difficult to learn and use.Examples:

Assembly language, Machine language etc.

High Level Languages.

High level languages are those which are closer to human

languages like English and far from machine language.

Advantages

Programmes are easily readable and easy to write as well. Languages are easily learnt and used. Programmes are portable i.e. programmes are hardwareindependant.Disadvantages.
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Programmes require more time to run than low languagesprogrammes.

Programmes are not highly efficient.High level languages can be further subdivided into Procedural

languages and Object Oriented Languages.

Examples:

FORTRAN, PASCAL, COBOL

C language is somewhat between high level and low level

languages.

The C Language

C is somewhat between high level languages and low levellanguages.

Authors of c are Brian.W.Kernighan and Denis M.Ritchie. Both the authors wrote c to exploit native capabilities of

implemented computer.

Programmes are much efficient and almost nearer to lowlanguage programmes

Portable programmes can be written as well C falls in block structured, procedural language category of

high level languages.

Source Code

Programme written by a programmer using any language is

called source code. This is a text file only understandable to

human beings. This code is not understandable to computers

because a computer can understand only machine language.

Compiler-Compilation

The source code that is written by a programmer is not

understandable to computer. To make it understandable to

computer, this source code should be translated to such a language

that can be easily understood to computer so that the computer

may know what we want it to be done. The process of translation

into such a form is called Compilation and a programme that

performs this job is called Compiler. Almost every language comes

with its own builtin compiler.

Object Code

When source code is translated into such a code that is

understandable to computer. This resulting code is called Object


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code. Through this code computer knows what we want to do via

programme.

Integrated Development Environment (IDE).

IDE of any language is such environment where you can

write,compile,debug and run your programmes.So an environment that offers you all these features is called

Integrated Development Environment as its name implies it

integrates all above features from writing a programme to running a

programme and you dont need to switch different programmes to

do all these tasks.

Some important shortcuts for c language

F1

F2

F3

F4

F5

F6

F7

F8

F9

F10

ALT+0

ALT(1..9)ALT+F1

ALT+F3

ALT+F4

ALT+F5

ALT+F7

ALT+F8

ALT+F9

CTRL+DEL

CTRL+F1CTRL+F2

CTRL+F3

CTRL+F9

Help

File Save

File Open

Run Go To Cursor

Window Zoom

Window Next

Run Trace Into

Run Step Over

Compile(make exe)

None;takes you to menu bar

Window List

None;displays window through 1 to 9Help previous topic

Window close

Debug inspect

Window user screen

Search previous error

Search next error

Compile to obj

Edit clear

Help topic searchRun programme reset

Debug call stack

Compile+Run


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Basic Structure Of C Programme

Let us investigate the various elements of c programme.

#include

void main(void)

{

Cout


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Variables are usesd so that the same space (memory location)

can hold different values at different times. You can take an

example of a mathematical expression which contains three

variables x,y,z. The value of x is depending on value of y and z i.e.

x=y+z

Whenever this expression is manipulated, for example we putdifferent values for y and z, so their addition put new value in x

everytime, let say we give y=2 and z=3 for first time, so x will hold

5 and again we change y=4 and z=8 then x=12. Same is the case

with memory variables, everytime the programme runs, variables

can hold different data.

Constants and Variables

The power of computer language comes from the ability to

use variable, which can hold many different values in programmes

statement. Let us write our previous programme again to use a

variable instead of a constant

#include

void main(void)

{

int num;

num=2;cout


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int rollno,age,clas;

When you define a variable, the compiler set aside an

appropriate amount of memory to store that variable. For an

integer variable, compiler will set aside two bytes of memory.

These two bytes are larger enough to hold numbers from 32768 to

32768. Actually the amount of memory used for a variable isdependent on the particular computer system and compiler being

used. Turbo c++ operates with two bytes. Borland c++ compiler

operates with four bytes i.e. you can make an integer variable to

hold values from 2147483648 to 2147483647. Anyhow, turbo c++

compiler is under our discussion, so we will follow as 2-byte for an

integer variable.

Some Other Data Types or Variable Types

There are, of course, other types of variables besides integer, we

shall sumamrize them here and then give examples of the uses of

the more common types.

Type Name Memory

Space(bytes)

Range Exampl

es

Int/signed int 2 -32768 to 32767 5,10,45

55Char 1 -128 to 128 a,1,

10

Long int 4 -2147483648 to

2147483647

35540

Float 4 1038to 10-38

(precision6 digits)

2.12546

Double 8 10308to 10-308

(pricision 15 digits)

5.15246

8

Long double 10 10-4932to 104932(precision 19 digit)

Short 2 Same as int Same as

int

Unsigned int 2 0 to 65535

Signed char 1 0 to 255

Signed char 1 -128 to 127

How To Initialize Variables

It is possible to combine a variable definition with an

assignment operator(=) so that a variable is assigned a value at the

same time it is defined. For example the following programme:-


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#include

void main(void)

{int event=5;

char heat=C;

float time=27.25;

cout


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\ Double quote

\\ Backslash

\a Beep

\xdd ASCII code in hexadecimal notation, each d

represents a digit.

\odd ASCII code in octal notation, each d represents a

digit.

The Cin operator

cout is an input operator unlike cout that was output. cin is

an input operator so that it will be used to store data in memory.

Here is a programme that uses cin.

#includevoid main(void)

{

float years,days;

coutyears;

days=years*365;

cout


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#include

void main(void)

{

int ftemp,ctemp;

coutftemp;

ctemp=(ftemp-32)*5/9;

cout


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Increment Operator

C/C++ uses another operator that is not common in other

languages, the increment operator. Consider the following

programme.

#include

void main (void)

{

int num=0;

cout


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#include

void main(void)

{

int age;

age=15;

cout


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real life, such as going to the movies and eating a good dinner.

Programming is the same way; we frequently need to perform an

action over and over, often with variations in the details each time.

The mechanism that meets this need is the loop.

There are three major loop structures in c; the For loop, the

While loop and a cousin of the while loop called do while loop.

FOR Loop

It is often the case in programming that you want to do

something a fixed number of times. Perhaps you want to calculate

the paychecks for 120 employees or print the squares of all the

numbers from 1 to 50. The for loop is ideally suited for such cases.

Lets look at an example of a for loop.

#include

void main (void)

{

int count;

for(count=0; count


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Multiple Statements in a loop

Two or more statements can also be used in the body of for

loop. This kind of statement, consisting of more than one

statements is called compound statement and a compound

statement is always enclose in braces.Void main(void)

{

int count,total;

for(count=0; total=0;count


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Cout


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total=


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Void main(void)

{

int I;

char ch;

for(I=0; I


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The Do While loop

This loop is similar to the while loop. The difference is that in the

do loop the test condition is evaluated after the loop is executed

rather than before.

Void main(void){

int count=0;

int total=0;

do

{

total=total+count;

cout


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Decision Making Structures

Computer languages, too, must be able to perform difficult sets of

actions depending on circumstances. C has three major decision-

making structures, the IF statement, the IF-ELSE statement and the

SWITCH statement. A fourth, somewhat less important structure isthe conditional operator.

The IF statement

Like most languages, c uses the keyword if to introduce the basic

decision-making statement.

Void main(void)

{

char ch;

cout


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Example Example

Void main(void)

{

char ch;

cout


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ELSE-IF construct

Void main(void)

{

int average;

coutaverage;if((average>60)&&(average


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SWITCH Statement

The switch statement is similar to the else if construct but has more

flexibility and a clear format.

Vod main(void)Float num1=1.0,num2=1.0;

Char op;

While(!(num1==0.0 && num2==0.0))

{

Coutnum1>>op>>num2;

switch(op)

{

case+:

cout


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Max=(num1>num2)? Num1:Num2;

Two values num1 and num2 are being compared. If num1 is greater

than num2 then it will be assigned to the max variable otherwise

num2, which is obviously greater than num1 will be assigned to

max. In any case at the end max would have the larger value of

two given values.

FUNCTIONS

A computer programme cannot handle every task alone.

Instead, it calls on other program-like entities called functions in c-

to carry out specific task.

Simple function

Void line(void);

Void main(void)

{

line();

cout


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The line is declarator. The first void means that line could not

return anything and the second void means that it takes no

arguments.

Note that the declarator does not end with a semicolon. It is not a

programme statement whose execution causes something to

happen. Rather it tells the compiler that a function is beingdefined.

The function definition continues with the body of the function: the

program statements that do the work.

2.Calling the Function.As with the c library function we have seen such as cout and

getch(), our user written function line() is called from main(),

simply by using its name, including the parenthesis following the

name. The parenthesis let the compiler know that you are referring

to a function and not a variable or something else. Calling a

function like this is a c statement, so it ends with a semicolon.

line ();

this function call causes control to be transferred to the code in the

definition of line(). This function call causes drawing its rows of

square on the screen, and then return to main(), to the statement

immediately following the function call.

3.Function Prototype.This is the line before the beginning of main():

Void line (void);

This looks very much like the declarator line at the start of the

function definition, except that it ends with a semicolon. What is

purpose?

You have already seen many examples of variables in c programs.

All the variables were defined by name and data type before theywere used. A function is declared in a similar way at the beginning

of a programme before it is called. The function definition (or

prototype-mean same thing) tells the compiler the name of the

function, the data type, the function returns (if any) and the

number and data types of the functions arguments (if any).

Local or AutomaticVariables

The variable j used in the line() function is known only to

line(); it is invisible to the main() function. If we add the following

statement to main () (without declaring a variable j)

Printf(%d,j);

We would get a compiler error because main() would know nothing

about this variable. We could declare another variable also called j


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in the main(), it would be a completely separate variable, known to

main() but not to line(). Variables defined in a function are

unknown outside the function. The question of which function

know about a variable and which does not is called visibility of a

variable. A local variable will be visible to the function it is defined

in but not to others.A local variable used in this way in a function is known in c as

an automatic variable, because it is automatically created when a

function is called and destroyed when the function returns. The

length of time a variable lasts is called its lifetime.

Functions that return a value.

A function that uses no arguments but returns a value perform

a similar role as you call 14 through your telephone set and it

returns current time. So you are saying nothing just calling and it

gives you back time because computer is on other side. You call

the function, it gets a certain piece of information and returns it to

you. The function getche() operates in just that way, you call it-

without giving it any information and it returns the value of the first

character typed on the keyboard.

Suppose we want to write a programme that takes upper case

letters from us and returns us lower case letters.

Programme

Char getlc(void);

Void main(void);

{

char chlc;

cout


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ch=getche();

if(ch>64 && ch64 && ch


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Void bar(int);

Void main(void)

{

Cout


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External Variable or Global Variable

It is sometimes desirable to use a variable known to (that is

visible to) all the functions in a programme, rather than just one.

In this case we have external variable sometimes called globalvariable.

Void oddeven(void);

Void negative(void);

Int keynumb;

Void main(void)

{

Coutkeynumb;

oddeven();

negative();

}

void oddeven(void)

{

if(keynumb%2)

cout


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Num=44;

You are asking the compiler to translate this code into

machine language instructions that can be executed by the

microprocessor chip in the computer. Thus most of your listing

consists of instructions to the microprocessor. Preprocessor

directives, on the other hand, are instructions to the compileritself. Rather than being translated into machine language, they

are operated on directly by the compiler before the compilation

process even begins; hence the name preprocessor.

The #define Directive.

The simplest use for the #define directive is to assign names

(Days,Pi, for example) to constants such 365 or 3.1415 etc.

#include

#define PI 3.1415

void main(void)

{

int radius,area;

coutradius;

area=PI*radius*radius;

cout


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Int func(void);

Void main(void)

{

int j;

for(j=0; j

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