Comment:-
It is a non executable statement i.e. it doesn’t have any effect on the
program. This statement is mainly used to indicate purpose of a program, a
function, a block etc. There are 2 types of comments statement:-
I.
Single line comment:- Comment is written
in 1 line only with 1 set of ‘//’.
example:- // program to fing sum
of
// two numbers
II.
Double line comment:- Comment can be
written in multiple lines.
example:- /*program to find sum
of two numbers*/
Header files:-
These are used to invoke library functions such as pow(), sqrt() etc and use
the objects cin, cout etc.
example:-
#include <math.h>
#include “math.h”
The header file written within
angular brackets is searched from default directory i.e. the directory created
during installation of C++.
The header file written within
angular brackets is searched from default directory as well as from the current
directory i.e. the directory created by user. Please note that now a days in modern C++ compiler instead of <iostream.h> <iostream> is used.
Main function:-
The execution of C++ program starts and ends within the main() function. This
function derives statements, library functions, user defined functions etc used
in program. In C++ each function is written with return type hence main is
generally written as
void
main()
or
int
main() /*
assuming return 0; is present in main function*/
Declaration:-
The variables or constants used in a program should be declared with a
datatype.
Example:- int
a,b,c; const int n=12;
Input statement:-
This statement is written with input functions such as scanf(); gets(); cin;
etc.
cin is an object defined in header file iostream.h ‘or’
istream.h and hence header file iostream.h ‘or’ istream.h should be included to
invoke the object cin.
syntax:-
cin>>a;
>> is called extraction operator.
cin>>a>>b>>c;
The above format is used to input a set of values. Here
a,b,c are variables.
Processing
statement:-These statement includes assignment statement, conditional
statement, statement for calling functions etc.
example:- a=3.14*r*r;
x=sqrt(y);
Output statement:-
These statements display the result on the screen. The function printf();
puts(); and the object cout is used to display results. cout is an object
defined in header file iostream.h ‘or’ istream.h and hence header file iostream.h
‘or’ istream.h should be included to invoke the object cout.
syntax:- cout<<a;
<< is called insertion operator
Now it’s time for some simple examples.
/*Program to find perimeter and area of rectangle*/
#include <iostream.h>
#include <conio.h>
void main()
{
float l,b;
clrscr();
cout <<"Enter
length and breadth";
cin>>l>>b; //
l and b are stored in memory
float a=l*b;
float p= 2*(l+b);
cout<<”Area=”<<a<<endl; //endl is used to send cursor to
cout<<”Perimeter=”<<p; // new line or to print “Enter”
getch();
}
/*Program to read time in second and display in hours,
minutes and seconds.*/
#include <iostream.h>
#include <conio.h>
void main()
{
int
s,hh,mm,ss;
clrscr();
cout<<”Enter time
in seconds”;
cin>>s;
hh=s/3600;
mm=(s%3600)/60; // % is used to find remainder
ss=(s%3600)%60;
cout<<”Time is”<<hh<<”hours”<<mm<<”minutes”<<ss<<"sec";
getch();
}
Exercise:-
Q. Write a program in C++ to swap two values without using a
third variable.
Q. Write a program in C++ to read length, breadth and height
of a cuboid and display its volume and surface area.
Q. Write a program in C++ to read 3 sides nd display area of
triangle.
Hint area= sqrt(s*(s-a)*(s-b)*(s-c))
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