LOOPING
4.1 Basic element of Loop-there are three basic elements of the loop:-
Initializations , test expression, update expressions
Initialization are the statement which specify what should be the initial value of the variable which is been used to control the loop
Test expression is the condition which specifies that loop will continue or not.
Update expression is the statement which changes the value of the control variable as per requirement of the program.
4.2 Explain While statement
The while is a looping statement. Looping statements control execution of a series of other statements, causing part of a program to execute repeatedly as long as a certain statement is met.
while(test expression)
{
// program statement(s)
}
Ex1:- num=1;
while(num<=5)
{
System.out.print(num+” “);
num --
}
Output :- 1 2 3 4 5
Pragram 1.
program to input a number and display factorial of it.
import java.util.*;
class check8
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int n,fact,i;
System.out.println(“enter a number”);
n=Sn.nextInt();
fact=1;
i=1;
while(i<=n)
{
fact=fact*i;
i=i+1;
}
System.out.println(“factorial of “+n+” is “+fact);
}
}
Pragram 2.
program to input a number and find its sum of digit, number of digit, reverse of number
import java.util.*;
class check7
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int dig,num,rev,len,sum,cp;
System.out.println(“enter a number”);
num=Sn.nextInt();
cp=num;
sum=0;
rev=0;
len=0;
while(cp!=0)
{
dig=cp%10;
sum=sum+dig;
len++;
rev=rev*10+dig;
cp=cp/10;
}
System.out.println(“length of number ”+len);
System.out.println(“sum of digits ”+sum);
System.out.println(“sum of digits ”+rev);
}
}
4.3 DO- WHILE STATEMENT:-
This loop is similar to the while loop except the test expression occurs at the bottom of the loop. this ensures that the body executes at least one time.
Syntax:- do
{
Statement(s);
}while(test expression);
It will repeat statements given in the loop till condition given with it is true.
Exmple
int num=10;
do
{
System.out.println(num);
num--;
}while(num>=1);
This loop will print numbers from 10 to 1.
4.4 Explain the term the for loop with an example [2005]
THE FOR LOOP:- The for loop is easy to use, normally we use for loop when number of times statements is to be repeated is known. The for loop has initialization, test expression, update statement at the beginning of the loop.
Syntax:-
for(initialization;condition;increment)
{
Statement(s)
}
In for loop all these three loop control statements are optional.
Example
for(i=1;i<=10;i++)
{
System.out.println(i);
}
it will display numbers from 1 to 10.
Example 2
for(i=1,j=2;;i<=5;i++,j++)
{
System.out.print(i+”/”+j+”+”);
}
System.out.print(“\b”);
Above given loop will display
1/2+2/3+3/4+4/5+5/6
Example 3
for(i=1;i<=10;i++);
System.out.print(i);
It will display 11
Example 4
for( ; ; )
{
System.out.println(“hello”);
}
It will display hello infinite times
4.5 EMPTY LOOP /TIME DELAY LOOP
The loop which do not have body with it is called empty loop this type of loop are used to give some interval before starting some process.
Example
for(i=1;i<=1000000;i++);
System.out.println(“computer “);
Here it will keep counting 1to 1000000 then display given message .
4.6 State one similarity and one difference between while loop and do while loop. [2005]
Similarity:- Both are looping statement they execute given statement till given condition is satisfied.
Difference:- While is an entry control loop. condition is checked first then body of the loop get executed. Do-while is exit control loop. Body of the loop executes first then condition is checked
4.7 Break: The break statement is used in many programming languages such as c, c++, java etc. Some times we need to exit from a loop before the completion of the loop then we use break statement and exit from the loop and loop is terminated. The break statement is used in while loop, do - while loop, for loop and also used in the switch statement.
Example
for(i=1;i<100;i++)
{
if(i%9==0)
break;
System.out.println(i)
}
It will display number from 1 to 8 as soon as i will become 9 loop will terminate.
4.8 Continue: The continue statement is used in many programming languages such as C, C++, java etc. Sometimes we do not need to execute some statements under the loop then we use the continue statement that stops the normal flow of the control and control returns to the loop without executing the statements written after the continue statement. There is the difference between break and continue statement that the break statement exit control from the loop but continue statement keeps continuity in loop without executing the statement written after the continue statement according to the conditions
Example
for(i=1;i<100;i++)
{
if(i%9==0)
continue;
System.out.println(i)
}
It will display number from 1 to 99 except numbers which are divisible be 9 because as soon (i%9==0) condition will be true it will skip display statement.
4.9 RETURN STATEMENT: The return statement can be used to cause execution back to the caller to the method. Thus the return statement immediately terminates the method in which it is executed.
4.10 Explain break and continue statements. [2005] [2008]
break statement sends the control out of the loop. continue statement skips part of loop and goes for next iteration.
for(i=1;i<10;i++
{
if(i%2==0)
continue;
if(i==9)
break;
System.out.print(i);
}
in above example when i is even number then it will skip part of program and go for next iteration and when i is 9 it will terminate loop.
output will be 1357
4.11 DIFFERENCE BETWEEN WHILE AND DO-WHILE
WHILE
|
DO-WHILE
|
The while loop will not execute at all if the condition is not satisfied
|
The do while loop will execute at least once.
|
The while loop checks the condition first and then the execution begins
|
The do-while check the condition after executing the loop once
|
4.12 DIFFERENCE BETWEEN FOR AND WHILE LOOP
FOR
|
WHILE
|
It is used when we know in advance how many repetitions are to be done
|
It is used when we do not know the number of repetitions are to be done.
|
The initialization, condition check and update is done at one line.
|
Here initialization, condition check and update is done at difference places.
|
Find and correct the errors in the following program segment:- [2006]
int n[]=(2,4,6,8,10);
for(int i=0;i<=5;i++)
System.out.println(“n[“+i+”]=”+n[i]);
The corrected program segment is:-
int n[]={2,4,6,8,10};
for(int i=0;i<5;i++)
System.out.println(“n[“+i+”]=”+n[i]);
Find the output of the following program segment, when: [2006]
i)val=500
ii) val=1600
int val,sum,n=550;
sum=n+val>1750?400:200;
System.out.println(sum);
Output:- 200 for val =500
IMPORTANT POINTS
ü The statement within the block is executed one after the other. This type of structure is called sequential structure.
ü Use of goto statement creates an unconditional jump within program.
ü Control structure is used when tranfer of control takes place to the other part of the program depending on some conditon.
ü Java offers three selection statements: if,if...else and switch.
ü While if statement checks only for the condition that evaluates true, if...elsestructure checks for both truth and falsity of a condition.
ü The switch structure in Java consists of series of case keyword.
ü Each of the case value must be a unique literal constant and not a variable.
ü break statement is used to skip out of switchstructure.
ü Switch structure is an efficient way of writing multiple if statements that contains onlyequality conditions of integral values.
ü Repetitive statements in programming are called iteration or looping.
ü In Java the looping statements for, while anddo...while are used for performing iteration.
ü Initialization part of the loop contains assignment of value to a control variable.
ü Condition part of the loop is to test whether a boolean expression evaluates to true or false.
ü Modification part is used for updating the initial value of the control variable.
In nested loops the iteration of innermost loop is done first and the Pragram 2.
ü outermost at the end.
ü For executing a statement or a block of codes repeatedly a specified number of times for loop is used.
ü while and do…while loops can be used where the number of iteration is not known before hand.
ü break statement skips the rest of the statement of the body of the loop and exits the loop before the iteration is completed.
ü continue statement forces to skip the rest of the statement of the body of the loop before the loop finishes the iteration and passes control to execute the next iteration of the loop.
ü break and continue statements used withlabel can transfer control to any part of the program.
ü When break and continue statements are used within nested loops the inner loop gets affected.
EXAMPLE PROARAMS
Program 3.
program to display first 10 terms of fabonacci series:-
0,1,1,2,3,5,8,13,21,34
class febo
{
public static void main(String args[])
{
int i,fn,sn,cu;
fn=0;
sn=1
System.out.print( fn+”\t”+sn+”\t”);
for(i=3;i<=10;i++)
{
cu=fn+sn;
System.out.print( cu+”\t”);
fn=sn;
sn=cu;
}
}
}
Program 4.
program to input a number and display it is prime or not.
import java.util.*;
class checkprime
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int num,i,ctr;
ctr=0;
System.out.println( “enter a number”);
num=Sn.nextInt();
for(i=1;i<=num;i++)
{
if(num%i==0)
ctr++;
}
if (ctr<=2)
System.out.println( num+”is prime);
else
System.out.println( num+”is not prime);
}
}
Program 5
program to check a number is Armstrong or not
import java.util.*;
class armstrong
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int num,sum,i,dig;
System.out.println( “enter a number”);
num=Sn.nextInt();
sum=0;
for(i=num;i!=0;i=i/10)
{
dig-i%10;
sum=sum+dig*dig*dig;
}
if(sum==num)
System.out.println( num+”is Armstrong”);
else
System.out.println( num+”is not Armstrong “);
}
}
Program 6
program to input Two numbers and display highest common factors of the numbers using long division method.
import java.util.*;
class high
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int a,b,x,y,r;
System.out.println( “enter two number”);
a=Sn.nextInt();
b=Sn.nextInt();
if(a<b)
{
x=a;
y=b;
}
else
{
x=b;
y=a;
}
while(true)
{
r=y%x;
if(r==0)
break;
y=x;
x=r;
}
System.out.println(“hcf of “+a+” and “+b+ ” is “+x);
}
}
Program 7
program to input Two numbers and display highest common factors of the numbers using long division method.
import java.util.*;
class high
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int a,b,h;
System.out.println( “enter two number”);
a=Sn.nextInt();
b=Sn.nextInt();
for(i=1;i<=a;i++)
{
if(a%i==0 && b%i==0)
h=i;
}
System.out.println(“hcf of “+a+” and “+b+ ” is “+h);
}
}
Program 8
program to input Two numbers and display Least common Mutiple(LCM) of the numbers using long division method.
import java.util.*;
class high
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int a,b,lcm;
System.out.println( “enter two number”);
a=Sn.nextInt();
b=Sn.nextInt();
lcm=a;
while(lcm%b!=0)
{
lcm=lcm+a;
}
System.out.println(“lcm of “+a+” and “+b+ ” is “+lcm);
}
}
Program 9
program to input numbers till the users choice find sum of even, odd numbers.
import java.util.*;
class user
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int num,ev=0,od=0
char ch=’y’;
while(ch==’y’ || ch==’Y’)
{
num=Sn.nextInt();
if(num%2==0)
ev=ev+num;
else
od=od+num;
System.out.println( “press y to continue”);
ch=Sn.next().charAt(0);
}
System.out.println( “sum of even”+ev);
System.out.println( “sum of odd”+od);
}
}
Program 10
Program to display prime number between 1 to 50
public class Break{
public static void main(String[] args){
int i,j;
System.out.println("Prime numbers between 1 to 50 : ");
for (i = 1;i < 50;i++ ){
for (j = 2;j < i;j++ ){
if(i % j == 0)
{
break;
}
}
if(i == j)
{
System.out.print(" " + i);
}
}
}
}
public static void main(String[] args){
int i,j;
System.out.println("Prime numbers between 1 to 50 : ");
for (i = 1;i < 50;i++ ){
for (j = 2;j < i;j++ ){
if(i % j == 0)
{
break;
}
}
if(i == j)
{
System.out.print(" " + i);
}
}
}
}
//output
The Prime number in between 1 - 50 :
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
Program 11
menu driven program to input a number and display is perfect or not , palindrome or not.
import java.util.*;
class menu
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int num,i,dig,rev,sum,choice=1;
while(choice!=0)
{
System.out.println( “1 . perfect number”);
System.out.println( “2. palindrome number”);
System.out.println( “0. exit”);
System.out.println( “enter your choice”);
choice =Sn.nextInt();
switch(choice)
{
case 1: System.out.println( “enter a number”);
num=Sn.nextInt();
sum=0;
for(i=1;i<num;i++)
{
if(num%i==0)
sum=sum+i;
}
if (sum==num)
System.out.println(num+” is perfect no.”);
else
System.out.println(num+” is not perfect no.”);
Break;
case 2: System.out.println( “enter a number”);
num=Sn.nextInt();
rev=0;
for(i=num;i!=0;i=i/10)
{
dig=i%10;
rev=rev*10+dig;
}
if(rev==num)
System.out.println( num+” is palindrome”);
else
System.out.println( num+” is not palindrome”);
break;
case 0 : break;
default: System.out.println( “invalid option”);
break;
}
}
}
}
Program 12
menu driven program convert temperature from Fahrenheit to Celsius and Celsius to Fahrenheit [2007]
import java.util.*;
class menu
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int choice=1;
double cel,fah;
while(choice!=0)
{
System.out.println( “1 . Fahrenheit to Celsius”);
System.out.println( “2. Celsius to Fahrenheit”);
System.out.println( “0. exit”);
System.out.println( “enter your choice”);
choice =Sn.nextInt();
switch(choice)
{
case 1: System.out.println( “enter temp in Fahrenheit”);
feh=Sn.nextDouble()
cel=(feh-32)*5/9;
System.out.println(cel+” celsius”);
break;
case 2: System.out.println( “enter temp in Celsius”);
cel=Sn.nextDouble()
feh=(feh*9/5)+32;
System.out.println(feh+“Fahrenheit”);
break;
case 0 : break;
default: System.out.println( “invalid option”);
break;
}
}
}
Program 13
program to find sum to given series using menu driven program
1+(1+2)/(1*2)+(1+2+3)/(1*2*3)+…….n terms
X+X2/3!+X3/3!+X4/4!..........................XN/N!
import java.util.*;
class menu
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int X,N,choice.i,p,q,f;
double sum,term;
while(choice!=0)
{
System.out.println( “1 . Series 1”);
System.out.println( “2. Series 2”);
System.out.println( “0. exit”);
System.out.println( “enter your choice”);
choice =Sn.nextInt();
switch(choice)
{
case 1: System.out.println( “enter a number”);
n=Sn.nextInt();
p=0; q=1; sum=0.0;
for(i=1;i<=n;i++)
{
p=p + i ;
q=q * i;
sum=sum+ p/q;
}
System.out.println( “sum =”+sum);
break;
case 2 : System.out.println( “enter x and n”);
x=Sn.nextInt();
n=Sn.nextInt();
f=1; sum=0.0;
for(i=1;i<=n,i++)
{
f=f* i;
term=Math.pow(x,i)/f;
sum=sum+term;
}
System.out.println(sum);
break;
case 0: break;
default: System.out.println( “invalid choice”);
break;
}
}
}
}
Program 14
program to display given pattern
55555
54444
54333
54322
54321
class pattern
{
public static void main(String args[])
{
int x,y,z;
for(x=5;x>=1;x--)
{
for(y=5;y>=x;y--)
System.out.print( y);
for(z=1;z<x;z++)
System.out.print(x);
System.out.println( );
}
}}
Program 15
//program to display given pattern
1
212
32123
4321234
543212345
class pattern
{
public static void main(String args[])
{
int x,y,z,sp,s;
for(i=1,sp=4;i<=5;i++,sp--)
{
for(s=1;s<=sp;s++)
System.out.print(“ “);
for( y=i;y>=1;y++)
System.out.print( y);
for(z=2;z<=i;z++)
System.out.print( z);
System.out.println( );
}
}}
Program 16
Write a program to print the sum of negative number, sum of positive even and sum of positive odd number from a list of number(N) entered by the user. the list is terminates when the user enter a zero. [2005]
import java.util.*;
class check
{
public static void main(String args[]) throws Exception
{
buffer
int n,sn=0,se=0,so=0;
for(;;)
{
System.out.println"enter a number 0 to stop");
n=Sn.nextInt();
if(n==0)
break;
if(n<0)
sn+=n;
else if(n %2==0)
se+=n;
else
so+=n;
}
System.out.println("sum of negative\t"+sn);
System.out.println("sum of positive even\t"+se);
System.out.println("sum of positive odd\t"+so);
}
}
Program 17
Write a program to calculate and print the sum of odd numbers and the sum of even numbers for the first n natural numbers.[2006]
The integer n is to be entered by the user.
import java.util.*;
class prog1
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int even=0,odd=0,i,n;
System.out.println(“Enter a number”);
n=Sn.nextInt();
for(i=1;i<=n;i++)
{
if(i%2==0)
even=even+i;
else
odd=odd+i;
}
System.out.println(“Sum of Even “+even);
System.out.println(“Sum of Odd “+odd);
}
}
}
Program 18
Write a program that outputs the results of the following evaluations based on number entered by the [2006]
User:-
i. Natural Logarithm of the number.
ii. Absolute value of the number.
iii. Square root of the number.
iv. Random numbers between 0 and 1.
import java.util.*;
class menu
{
public static void main(String args[]) throws Exception
{
Scanner Sn=new Scanner(System.in));
int choice=1,n;
double cel,fah;
while(choice!=0)
{
System.out.println( “1 Natural Logarithm of the number.”);
System.out.println( “2. Absolute value of the number”);
System.out.println( “3. Square root of the number”);
System.out.println( “4. Random numbers between 0 and 1”);
System.out.println( “0. exit”);
System.out.println( “enter your choice”);
choice =Sn.nextInt();
switch(choice)
{
case 1: System.out.println( “Enter a number”);
n =Sn.nextInt();
System.out.println(“Natural Logarithm =\t”+Math.log(n));
break;
case 2: System.out.println( “Enter a number”);
n =Sn.nextInt();
System.out.println(“Absolute value =\t”+Math.abs(n));
break;
case 3: System.out.println( “Enter a number”);
n =Sn.nextInt();
System.out.println(“Square Root =\t”+Math.sqrt(n));
break;
case 4: System.out.println(“Random Number =”+Math.random());
break;
case 0 : break;
default: System.out.println( “invalid option”);
}
}
}
}
Program 19:- . Write a program to calculate and print the sum of each of the following series
Sum(S)= 2-4+6-8+……..20
Sum(S)= x/2+x/5+x/8+x/11….. +x/20
(value of x to be input by the user.) [2008]
import java.io.*;
class abc
{
public static void main(String[] args) throws Exception
{
DataInputStream d=new DataInputStream(System.in);
int x,s,i;
s=0;
for(i=2;i<=20;i=i+2)
{
if(i%4==0)
s=s-i;
else
s=s+i;
}
System.out.println("Sum is series 1 is "+s);
System.out.println("Enter a number");
x=Integer.parseInt(d.readLine());
double sum=0.0;
for(i=2;i<=20;i=i+3)
{
sum=sum+(double)x/i;
}
System.out.println("Sum is series 2 is "+sum);
}
}
Program 20:- Write a menu driven program to accept a number form the user and check whether it is a palindrome or a perfect number.
Palindrome number:- a number is a palindrome which when read in reverse order is same as read in the right order. E.g 11,101,151 etc.
Perfect number:- a number is called perfect if it is equal to the sum of its factors other than the number itself. E.g – 6=1+2+3
import java.util.*;
class menu
{
public static void main(String[] args)throws Exception
{
Scanner Sn=new Scanner(System.in));
int ch=1,i,num=0,r;
while(ch!=0)
{
System.out.println("1. Palindrome number\n2. Perfect number");
System.out.println("0. exit\n Enter your choice");
ch=Sn.nextInt();
if(ch==1 || ch==2)
{
System.out.println("Enter a number");
num=Sn.nextInt();
}
switch(ch)
{
case 1 : r=0;
for(i=num;i!=0;i=i/10)
r=r*10+i%10;
if(r==num)
System.out.println("Palindrome");
else
System.out.println("Not Palindrome");
break;
case 2: r=0;
for(i=1;i<num;i++)
{
if(num%i==0)
r=r+i;
}
if(r==num)
System.out.println("Perfect no");
else
System.out.println("Not perfect");
break;
case 0: break;
default: System.out.println("invalid option");
break;
}
}
}
}
Ques Convert the following segment into equivalent for loop. [2008]
int i=1;
while(i<=20)
{
System.out.println(i+" ");
i++;
}
Ans;- int i;
for(i=1;i<=20;i++)
{
System.out.println(i+” “);
}
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