Iterative Statements (Looping
Statements)
Whenever we have to execute some statements (or expression)
for a certain number of time (or for a particular condition until it gets
false) we use Loops (Iterative
statements).
There are three types of Loop:
1)
While Loop
2)
Do-while Loop
3)
For Loop
While Loop: Provides
a mechanism of repeating one or more statements while a particular condition is
true.
Syntax:
Statement
a;
while(condition)
{
Statement block;
}
Statement b;
Initially the control of the program is at “statement a”à then condition is
checked à
if true (1) à
“statement block” will get executed à
if false (0) control will jump out of the while loop and “statement b“ will get executed.
Example: program to find sum of first 10 numbers:
#include<stdio.h>
#include<conio.h>
int main()
{
int i=0, sum =0;
while(i<=10)
{
sum=sum+I;
i=i+1; // here condition is getting updated.
//When value
of i
will be equal to 11,
// condition gets
false. And prinf() statement will get executed.
}
printf(“\n sum of first 10 numbers
= %d”,sum);
getch();
return 0;
}
Note: we did not put
semicolon at the end of while.
Do-while Loop:
is similar to the while Loop, but the only difference is that the condition is
tested after the Loop block. That means the Loop block will get executed at
least once even if the condition is false.
Syntax:
Statement
a;
do
{
Statement
block;
}
while(condition);
Statement
b;
Example:
#include<conio.h>
#include<stdio.h>
int
main()
{
int
i=0;
do
{
printf(“\n %d”, i);
i=i+1;
}while(i<=10);
getch();
return
0;
}
Now this code will print numbers from 0 to
11, not from 0 to 10.
Note: in Do-while
Loop, we always terminate while() with semicolon but not in the while Loop.
For Loop: for loop also provides us the
mechanism of repeating a task until a particular condition gets false.
Here the programmer exactly know that how many time the task
has to repeat.
How the for loop
is different from while and do while:
Here
the initialization of variable, checking condition, and updating condition is
written in a single line.
Syntax:
for(initialization;
condition; update)
{
Statement
block;
}
Statement
y;
Example :
Program
to print first n numbers using for loop.
#include<conio.h>
#include<stdio.h>
int main()
{
int a,n;
printf(“\n Enter the value of n “);
scanf(“ %d “,&n);
for(a=0;a<=n;a++)
{
printf(“\n
%d “, a);
}
getch();
return 0;
}
Mechanism :
11)
Firstly initialization of a=0;
22)
Check condition a<=10;
33)
If true à
get in the statement block. And print the value.
Then update the condition a=a+1; i.e. a=1;
Again check condition a<=10;
True: again get into the statement block and print.
And so on.
44)
If falseà
get out of the for loop(or statement block)
Note: there must be no semicolon after the for statement.
More about for loop:
11)
You can initialize and update more than one
variable,.( must be separated by the comma(,) )
int i,j;
For(i=0,j=1; i<5; i++,j++)
{
Statement;
}
22)
Multiple conditions can be use by logical
operators (&& or ||)
33)
If you have already initialize the variable then
you can skip initialization in the for statement.
int i=0;
for( ; i<10;i++)
44)
Similarly you can update condition inside the
block
int i=1;
for( ; i<10 ; )
{
Printf(“\n %d”, i);
i=i+3;
}
55)
If you do not provide any condition or a
condition which is always true. Then it becomes an infinite loop.
for( ; ; )
{
printf(“programming infinitum “);
}
Or
for(i=1;
i>0; i++) // infinite loop
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