Looping
Statements / Iterative Statements :
'A loop' is a part of code of a program which is executed
repeatedly.
A loop is used using condition. The repetition is done until
condition becomes condition true.
A loop declaration and execution can be done in following ways.
o Check
condition to start a loop
o Initialize
loop with declaring a variable.
o Executing
statements inside loop.
o Increment
or decrement of value of a variable.
*
TYPES OF LOOPING STATEMENTS :
Basically, the types of looping statements depends on the
condition checking mode. Condition checking can be made in two ways as : Before
loop and after loop. So, there are 2(two) types of looping statements.
·
Entry controlled loop
·
Exit controlled loop
1. Entry controlled loop :
In such type of loop, the test condition is checked first before
the loop is executed.
Some common examples of this looping statements are :
2. Exit controlled loop :
In such type of loop, the loop is executed first. Then condition
is checked after block of statements are executed. The loop executed atleat one
time compulsarily.
Some common example of this looping statement is :
While loop :
This
is an entry controlled looping statement. It is used to repeat a block of
statements until condition becomes true.
Syntax:
while(condition)
{
statements;
increment/decrement;
}
In above syntax, the
condition is checked first. If it is true, then the program control flow goes
inside the loop and executes the block of statements associated with it. At the
end of loop increment or decrement is done to change in variable value. This
process continues until test condition satisfies.
Program :
#include <stdio.h>
#include <conio.h>
void main()
{
int a;
clrscr();
a=1;
while(a<=5)
{
printf("\n Aasaan IT Classes");
a+=1 // i.e. a = a + 1
}
getch();
}
Output :
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
For loop :
This
is an entry controlled looping statement.
In
this loop structure, more than one variable can be initilized. One of the most
important feature of this loop is that the three actions can be taken at a time
like variable initilisation, condition checking and increment/decrement. The
for loop can be more concise and flexible than that of while and do-while
loops.
Syntax:
for(initialisation; test-condition; incre/decre)
{
statements;
}
In above syntax, the given three expressions are seperated by
';' (Semicolon)
Features :
o More
concise
o Easy to
use
o Highly
flexible
o More
than one variable can be initilized.
o More
than one increments can be applied.
o More
than two conditions can be used.
Program
:
#include <stdio.h>
#include <conio.h>
void main()
{
int a;
clrscr();
for(i=0; i<5; i++)
{
printf("\n\t Aasaan IT Classes"); // 5 times
}
getch();
}
Output :
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Do-While loop :
This
is an exit controlled looping statement.
Sometimes,
there is need to execute a block of statements first then to check condition.
At that time such type of a loop is used. In this, block of statements are
executed first and then condition is checked.
Syntax:
do
{
statements;
(increment/decrement);
}while(condition);
In
above syntax, the first the block of statements are executed. At the end of
loop, while statement is executed. If the resultant condition is true then
program control goes to evaluate the body of a loop once again. This process
continues till condition becomes true. When it becomes false, then the loop
terminates.
Note:
The while statement should be terminated with ; (semicolon).
Program
:
#include <stdio.h>
#include <conio.h>
void main()
{
int a;
clrscr();
a=1;
do
{
printf("\n\t Aasaan IT Classes"); // 5 times
a+=1; // i.e. a = a + 1
}while(a<=5);
a=6;
do
{
printf("\n\n\t Aasaan IT Classes"); // 1 time
a+=1; // i.e. a = a + 1
}while(a<=5);
getch();
}
Output :
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
Aasaan IT Classes
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