In order to perform
repeated task we use loops i.e. to execute a set of statements repeatedly or a number times we use loops. These are very important
in C++ .complex programs contain these loops almost every were. Loops generally
have a conditional statement.
So basically let us
consider your name being printed four times that is easy to perform as we can
write he cout statement four times but generally when
we use loops in C++ we generally do not know the number of times we have to
repeat the loop or maybe we need to print the statement 10000 times in that
case we cannot write these statements 10000 times.
A loop is a statement
which repeats a set of statements until a condition is met. These set of
statement are noting but are the statement enclosed in the loop.
There are basically
three main types of loops
While loop
Do-while loop
For loop
First we will take on
the while loop
Syntax:
while(condition)
{
Statements;
}
Here the condition is the
conditional statement which is checked every time the loop has to be executed
if the condition is true the loop is executed and if the condition is false
then the loop is not executed that means the statement s in side the lop are
not executed and the control passes to the statement after the while loop. Here
is an example:
#include <iostream.h>
void main()
{
int a,b=0;
cout<<”enter the number:”;
cin>>a;
while(b<a)
{
cout<<”sameer”;
b++;
}
}
This program prints the
string sameer a number of times. Here we need to
understand the meaning of the statement b++ which is actually incrementing the
value of a or to be more specific increases the value of a by one.
Here the condition b<a is checked before entering the loop the condition will be
true only till b is just one less than a. The logic of the program is that the
value of b will change from 0 to a-1 .so the number of times it value changes
is a so sameer will be printed a times. Logic of the
program is very important so before learning or writing the program please try
to make the logic of the program because without it the program cannot be made.
Here it is to be noted that if the value of a is entered 0 then the loop will
not be executed even ones this a advantage for some program but is a
disadvantage for some program but this feature is knocked out by the following
loop.
Syntax
do
{
Statements
}while(condition)
Example
#include <iostream.h>
void main()
{
int a,b=0;
cout<<”enter the number:”;
cin>>a;
do
{
cout<<”sameer”;
b++;
}
while(b<a)
}
This program is same as the
above but only thing is that it has a do-while loop
This is basically an exit controlled loop that means
that the condition is checked after the loop executes and depending on the
condition the next repetition is done.
The added advantage of
this loop is that if the user enters 0 in the above program then also the
string will be printed once as the condition will be checked after the
statement is executed difference between the while
loop and this loop is that in the first one the statement might not be executed
at all (if the condition is false from the very beginning), while in the second
it is always executed at least once. So if you want the statement to be
executed at least once than we you do-while loop.
for loop is the most important as well as the most
difficult loop to handle but the features that this loop offer is not met by
any other loop of course most of the time we can replace for by while loop but
using for is easy and it also has added advantage like easy debugging and
better data handling.
Syntax:
for(initialization ; condition ; incrementation
or decrementation)
{
Statements;
}
Initialization is the place were we can initialize any variable generally th variable which we use is initialized here.
Initialization we have already learnt I will not explain it again. You will see
how to use this in the example explanation.
Incrementation and decrementaton is the place where
we can put the increment and decrement command of the variable.
Concentrate on the
below example because the for loop is very important
#include<iostream.h>
void main()
{
int num,fact=1;
cout<<”enter the number:”;
cin>>num;
for(int
i=1;i<=num;i++)
{
fact=fact*i;
}
cout<<”factorial =”<<fact;
}
This program prints the
factorial of the input number. First we enter the number and initialize the
value 1 to the fact variable. The logic of the program is that we will multiply
the fact with all the number from 1 to the number whose factorial we need to
find. So we initialize a number i in the for loop and
we increment the value of I from 1 to num and multiply it to fact and store the
result in fact simultaneously as show in the for loop .here we observe that
the for statements are executed repeatedly
and incrementation of the variable takes place
automatically at the end of the program.
So basically following
things happen in for loop:
When the control
reaches the for loop the initialized value is stored as the command then the
condition is checked and accordingly the loop is executed .after the control
reaches the end of the loop the incrementation is done and the condition is checked again
and accordingly the loop is again executed and then again at the end the incrementaion is done and the condition checked. These
steps are followed till the condition becomes false once after which the loop
is exited and control passes to the statements following the for loop. It is to
be noted that if the condition is false in the very first execution then also
the initialization is executed.
Jump statements
These statements are used to transfer the control
from point to a different place in the program. These can be used by an able
programmer to play with the control of the program. These are very important for
making a program because a loop all alone can be used to make a simple program
but in order to make a complex program we need to make excellent use of these
jump statement.
Their are three types of jump statement they
are:
goto statement
goto is a command that can transfer the control from any point to any
possible point of the program. It has a goto
statement and a label.
Syntax:
goto label;
This
statement is used to tell the compiler to jump the control from this point to
the point were we place the label. Placing label is very easy as we can simply
place label in the following way.
Label:
Label is
any valid identifier (name) in C++ as we have discussed before.
It is to
be noted that generally a professional programmer does not use goto statement because while debugging it becomes very
frustrating and confusing for the programmer who debugs the program. It becomes
very difficult to find the label of the program and then continue the execution
from their.
break
Break
statement is used to exit the loop as soon as this statement is executed that
means this statement exits the loop in which it is used even though the
condition in the loop is true.
For example:
#include<iostream.h>
void main()
{
int a;
cout<<”enter
the number:”;
cin>>a;
for(int i=0;i<=a;i++)
{
if(a<0)
break;
cout<<i;
}
}
In this program the number a is entered and number from 1
to a are displayed on the screen but if the user enters 0 then the if statement
is executed and the condition becomes true and the break statement is executed
.as soon as the break statement is execute the control leaves the loop even
though the condition is true. Here we should understand oone
thing that the loop is exited and the next incrementation
is not done so value of I in the above program remains 0 even after the loop is
exited.
continue
This statement performs just the opposite task as performed
by the break statement in the above explanation .continue statement performs the
next incrementation on the loop ignoring all the statements after the continue
statement that means the statements after the continue statement are not
executed and as soon as ther control reaches the end
of the for loop the next incrementation is done and
the condition is checked and accordingly the loop is further executed.
For example:
#include<iostream.h>
void main()
{
int a;
cout<<”enter
the number:”;
cin>>a;
for(int i=0;i<a;i++)
{
if(i%2==0)
continue;
cout<<I;
}
}
The following program prints all the odd numbers from 0 to a .a is entered by the user. In this program every time the
value of I is even the if loop is executed so the continue statement is executed
which increments the value of I but does not execute these cout
statement as it follows the continue statement.
Now that you have learnt
these C++ concepts its time for you to write programs of your own and if you
want any help just put your program request and questions in the program
request. Yes you can put any theory question you have in the program request
page.
