## Java program for Pronic Number

According to  A pronic number is a number which is the product of two consecutive integers, that is, a number of the form n(n + 1). It is also called oblong number, rectangular number or heteromecic number.
Examples : 0, 2, 6, 12, 20, 30, 42, 56, 72, 90, 110, 132, 156, 182, 210, 240, 272, 306, 342, 380, 420, 462, 506, 552 etc

Method I

// Java program to find Pronic Number
import java.io.*;
class PronicNumber
{
public static void main(String args[]) throws IOException
{

int n, i;           // n for number and i for loop
boolean f=false;    // f for flag, initialize with false
System.out.print("Enter a number to find pronic or not : ");
for(i=1; i<=n; i++)
{
if(i*(i+1) == n)
{
f = true;
break;
}
}
// Checking the pronic number
if(f == true)
System.out.println(n+" is a Pronic Number.");
else
System.out.println(n+" is not a Pronic Number.");
}
}

Sample Output:
Enter a number to find pronic or not : 110
110 is a Pronic Number.
Enter a number to find pronic or not : 272
272 is a Pronic Number.
Enter a number to find pronic or not : 6
6 is a Pronic Number.
Enter a number to find pronic or not : 35
35 is not a Pronic Number.

Method II

// Java program to find Pronic Number
import java.io.*;
class PronicNumberWithFunction
{
int n, i;           // n instance variable for number and i for loop
boolean f=false;    // f instance for flag, initialize with false
boolean pronic()throws IOException
{
System.out.print("Enter a number to find pronic or not : ");
for(i=1; i<=n; i++)
{
if(i*(i+1) == n)
{
f = true;
break;
}
}
return f;
}
// Main method start
public static void main(String args[]) throws IOException
{
// Checking the pronic number
boolean f;
PronicNumberWithFunction ob = new PronicNumberWithFunction();
f = ob.pronic();
if(f == true)
System.out.println("A number is a Pronic Number.");
else
System.out.println("The number is not a Pronic Number.");
}
}

Sample Output:
Enter a number to find pronic or not : 12
The number is a Pronic Number.
Enter a number to find pronic or not : 130
The number is not a Pronic Number.

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## Selection Sort in Java

Selection sort is a very easy and simple sorting algorithm. It repeatedly selects the smallest or largest elements from the array and places it in the first position of the array. This process is repeated with the rest of the array. The second smallest or largest element is selected and put onto the next slot and this process is repeated till the end of the array. Time complexity is  O(n2)

import java.util.Scanner;
public class SelectoinSort {

public static void main(String arg[]) {
Scanner sc = new Scanner(System.in);
int number[] = new int[10];
int i, j, l, k = 0, m;
int t;
System.out.println("Enter integer");
for (i = 0; i < 10; i++) {
m = sc.nextInt();
if (m != 0) {
number[k] = m;
k++;
}
}
// Printing unsorted data
System.out.println("Unsorted order");
for (i = 0; i < k; i++) {
System.out.print(number[i] + " ");
}
// Sorting technique
for (i = 0; i < k; i++) {
for (j = i + 1; j < k; j++) {
if (number[i] >number[j]) {
t = number[i];
number[i] = number[j];
number[j] = t;
}
}
}
// Print sorted data
System.out.println("\n Sorted order");
for (i = 0; i < k; i++) {
System.out.print(number[i] + " ");
}
}
}

Sample output
Enter integer
50
65
90
66
45
21
45
65
25
89
Unsorted order
50 65 90 66 45 21 45 65 25 89
Sorted order
21 25 45 45 50 65 65 66 89 90

 SN Variables Type Description 1 main() void This is the main entry point of the program 2 number[] int int   array for the name 3 m int For checking zero 4 i, j int i and j are for loop 5 t int Use for a temporary variable

### Program to sort an array of strings using Selection Sort

import java.util.Scanner;
public class SelectionSortForString
{
public static void main(String arg[]) {
Scanner sc = new Scanner(System.in);
// String Array
String studentName[] = new String[10];
int i, j, l ;
String t;
System.out.println("Enter Student Name:");
for (i = 0; i < 10; i++) {
studentName[i]= sc.next();

}
// Printing unsorted data
System.out.println("Unsorted order");
for (i = 0; i < 10; i++) {
System.out.print(studentName[i] + " ");
}
// Sorting technique
for (i = 0; i <9; i++) {
for (j = i + 1; j < 10; j++) {
if (studentName[i].compareTo(studentName[j])>0) {
t = studentName[i];
studentName[i] = studentName[j];
studentName[j] = t;
}
}
}
// Print sorted data
System.out.println("\n Sorted order");
for (i = 0; i < 10; i++) {
System.out.print(studentName[i] + " ");
}
}

}

#### Analysis of Selection sort

Selecting the lowest element requires scanning all n elements (this takes n − 1 comparisons) and then swapping it into the first position. Finding the next lowest element requires scanning the remaining n − 1 elements and so on
(n-1) + (n-2) + (n-3) + ….. + (n-k) + 3 + 2 + 1
n(n-1)/2
O(n
2)

#### Bubble sort program in Java

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## Java Program to find Emirp Number

### Java program for Emirp Number

A number which is prime backward and forwards is called emirp number. Example: 13 and 31 are both prime numbers. Thus, 13 is an emirp number. Design a class Emirp to check if a given number is Emirp number or not. Some of the members of the class are given below:
Class name                 Emirp
Data members/instance variables:
n                               stores the number
reverse                     stores the reverse of the number
f                                stores the divisor
Member functions :
Emirp(int n)               to assign n = n, reverse = 0 and f = 2
int isprime(int x)         check if the number is prime using the recursive technique and return I if prime otherwise return 0
void isEmirp( )             reverse the given number and check if both the original number and the reverse number are prime. by invoking the function isprime(int) and display the result with an appropriate message
Specify the class Emirp giving details of the constructor(illt), int isprime(int) and void isEmirp().
Define the main( ) function to create an object and call the methods to check for Emirp number.

import java.io.IOException;
/**
* class Emirp
* ISC 2013 paper Question 08
*/
public class Emirp
{
// instance variables
private int n;      // For number
private int reverse;    // reverseeres number
private int temp;   // temporary variable

/**
* Constructor for objects of class Emirp
*/
public Emirp(int n)
{
// initialise instance variables
this.n = n;
reverse = 0;
temp = 2;
}

public int isPrime(int x, int i)
{

if(i==1){
return 1;
}
else
{
if(x%i==0)
return 0;
else
return isPrime(x,i-1);
}
}
void isEmirp()
{
int a,p1, p2;
temp = n;
while(n !=0 )
{
a = n % 10;
reverse = reverse * 10 +a;
n = n/10;
}
System.out.println(reverse);
p1 = isPrime(temp,temp/2);          // call the isPrime for the original number
p2 = isPrime(reverse,reverse/2);    // call the isPrime for the reverse number
if( p1 == 1 && p2  == 1)
{
System.out.println("Number is Emirp");
}
else
{
System.out.println("Number is not Emirp");
}
}
public static void main(String args[])throws IOException
{
int n;
System.out.println("Enter the number ");
Emirp ob = new Emirp(n);
ob.isEmirp();
}
}

Sample Output
Enter the number
13
31
Number is Emirp

Enter the number
14
41
Number is not Emirp

Enter the number
71
17
Number is Emirp
 Sl. No. Variable Name Data Type Purpose 1 n, reverse, temp int instance variables 2 Emirp() Constructor The constructor of Emirp class 3 isPrime(int, int) int Checking prime number or not (recursive method) 4 isEmirp() void Checking Emirp 5 a, p1, p2 int Local variable to isEmirp() method 6 in InputStreamReader The object of InputStreamReader class which exists in java.io package 7 br BufferedReader Use to create object br which exists in java.io package main() void Main function

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