Looping statements:
Types of Loops
Depending
upon the position of a control statement in a program, a loop is classified
into two types:
1. Entry controlled loop
2. Exit controlled loop
In an entry
controlled loop, a condition is checked before executing the body of a
loop. It is also called as a pre-checking loop.
In an exit
controlled loop, a condition is checked after executing the body of a loop.
It is also called as a post-checking loop.
The control
conditions must be well defined and specified otherwise the loop will execute
an infinite number of times. The loop that does not stop executing and
processes the statements number of times is called as an infinite loop. An
infinite loop is also called as an "Endless loop."
Following are some
characteristics of an infinite loop:
1. No termination condition is
specified.
2. The specified conditions never
meet.
The specified condition
determines whether to execute the loop body or not.
The while statement
It is an
entry-controlled loop. In while loop, a condition is evaluated before
processing a body of the loop. If a condition is true then and only then the
body of a loop is executed. After the body of a loop is executed then control
again goes back at the beginning, and the condition is checked if it is true,
the same process is executed until the condition becomes false. Once the
condition becomes false, the control goes out of the loop.
After
exiting the loop, the control goes to the statements which are immediately
after the loop. The body of a loop can contain more than one statement. If it contains
only one statement, then the curly braces are not compulsory. It is a good
practice though to use the curly braces even we have a single statement in the
body.
In while
loop, if the condition is not true, then the body of a loop will not be executed,
not even once.
Syntax:
while (condition)
{
statements;
}
Example:
#include<stdio.h>
#include<conio.h>
main()
{
int num=1; //initializing the variable
clrscr();
while(num<=10) //while loop with condition
{
printf("%d\n",num);
num++; //incrementing operation
}
getch();
}
The do … while statement
It is an exit-controlled
loop. The do…while loop checks the condition at the end of the loop.
This means that the statements inside the loop body will be executed
at least once even if the condition is never true. The do…while loop is mainly
used in the case where we need to execute the loop at least once. The do…while
loop is mostly used in menu-driven programs where the termination condition
depends upon the end user.
Syntax:
do
{
statements;
} while (condition);
Example:
#include<stdio.h>
#include<conio.h>
main()
{
int num=1; //initializing the variable
clrscr();
do
{
printf("%d\n",num);
num++; //incrementing operation
} while(num<=10); //while loop with condition
getch();
}
In the do…while
loop, the body of a loop is always executed at least once. After the body is
executed, then it checks the condition. If the condition is true, then it will
again execute the body of a loop otherwise control is transferred out of the
loop.
The for statement
A for loop
is a more efficient loop structure in 'C' programming. Like while loop it
is an entry-controlled loop. The main advantage of using this loop is that, one
can specify initialization, condition and increment / decrement operation on
single statement.
The general
syntax of for loop is
Syntax:
for (initialization; condition; incrementation or decrementation
)
{
statements;
}
Ø The initialization of the
for loop is performed only once.
Ø The condition is a
Boolean expression that tests and compares the counter to a fixed value after
each iteration, stopping the for loop when false is returned.
Ø The
incrementation/decrementation increases (or decreases) the counter by a set
value.
Example 1:
#include<stdio.h>
#include<conio.h>
main()
{
int i;
clrscr();
for(i=1;i<=10;i++) //for loop to print 1-10 numbers
{
printf("\n
I = %d",i); //to print the
number
}
getch();
}
Example 2:
#include<stdio.h>
#include<conio.h>
main()
{
int i;
clrscr();
for(i=10;i>=0;i--) //for loop to print 10 to 0 numbers
{
printf("\n
I = %d",i); //to print the
number
}
getch();
}
Example 3:
#include<stdio.h>
#include<conio.h>
main()
{
int i,no;
clrscr();
printf(“Enter a
number for Multiplication Table ”);
scanf(“%d”,&no);
for(i=1;i<=10;i++) //for loop to print 1-10 numbers
{
printf("\n
%d",i*no); //to print the
number
}
getch();
}
Example 4:
#include<stdio.h>
#include<conio.h>
main()
{
int i;
clrscr();
for(i=1;i<=10;i++)
{
if(i%2==0)
{
printf("\n Even Number = %d",i);
}
else
{
printf("\n Odd Number = %d",i);
}
}
getch();
}
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