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Java code that finds all factors of an interger inputted by a user using while loops [closed]

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So currently, I am working on a piece of code that will determine whether or not an integer is a prime number or not, and that works perfectly fine since I have tested it multiple times using different prime and non-prime integers. Now, I have to wrap it up by being able to list out all factors of any given integer and I just simply don't know what to do. Down below is my current program without the factors part that I need. I don't know where to start since I am not particularly good with "while loops" as we just learned about them today.
This is what I have to do, "The program should give the output of all factors of the integer using appropriate formatting so it the factors are clear.
It should output “The factors of (input) are:”
If the only factors of the integer input are 1 and itself, the program should state: “This is a prime number!” and if it is not
a prime number print nothing."
Any help with this would be greatly appreciated. Thanks!
import java.util.*;
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
System.out.println("What is the number that you have chosen?");
int num = console.nextInt();
int div = 2;
boolean run = false;
System.out.println("The factors of " + num + " are:");
while (div <= Math.sqrt(num)) {
if (num % div == 0) {
System.out.println(div + " , " + num/div);
div++;
run = true;
} else {
div++;
}
}
if (run == false) {
System.out.print("This is a prime number!");
}
}
}

For starters, you can use this:
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
while(factor<=num) {
if(num%factor==0) {
System.out.println("Found factor: "+factor);
}
factor++;
}
console.close();
So what does it do?
What you want to do is loop through every single number from 1 all the way to the number. This is illustrated from the statement in the while loop while(factor<=num).
To check whether it is a factor, we can use the statement if(num%factor==0). What does this mean? % means modulus, and basically it returns the remainder after you divide a number by another number. If the remainder is 0, we know it is a factor (it can divide successfully. If you don't know what a factor is, I recommend you study mathematics first).
We then increment factor by 1 each time, and check every number smaller than the user input, since there is no use of checking larger numbers (a number is never a factor of another if it is larger).
Test Run
10
Found factor: 1
Found factor: 2
Found factor: 5
Found factor: 10
If you want to implement prime number verification, you can do:
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
int factors=0;
while(factor<=num) {
if(num%factor==0) {
System.out.println("Found factor: "+factor);
factors++;
}
factor++;
}
if(factors==2) {
System.out.println("This is a prime number!");
}
console.close();
FINAL VERSION (according to your requirements)
Scanner console = new Scanner(System.in);
int num = console.nextInt();
int factor = 1;
int factors=0;
System.out.print("The factors of "+num+" are: ");
while(factor<=num) {
if(num%factor==0) {
System.out.print(factor+" ");
factors++;
}
factor++;
}
if(factors==2) {
System.out.println("This is a prime number!");
}
console.close();
Test Case
2
The factors of 2 are: 1 2
This is a prime number!

boolean isPrime = true;
for(int i = 2; i <= num/2; i++){
if(num % i == 0) {
System.out.println("The factors of " + num + " are:" + i);
isPrime = false;
}
}
if(isPrime) {
System.out.print("This is a prime number!");
}
Something I want you to think is why I am running the loop only till num/2 and not till num? Let me know if you can figure it out.

Change your while loop a bit to store the factors.
List<Integer> factors = new Arraylist<>();
int upperLimit = num/2
while (div <= upperLimit) {
if (num % div == 0) {
factors.add(div);
}
}
If you do this at the end of the loop, the factors variable which is a list will have all the factors fo the numebr in it. Now you can check if there are numbers in the list other than 1 or itself and if so, its not a prime.
Note: Instead of a list you can also have an array if you are not aware if what lists are in java.

I just did small changes to your code. This will give the answer in the best time complexity possible.
import java.util.*;
public class myClass{
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
System.out.println("What is the number that you have chosen?");
int num = console.nextInt();
int div = 2;
boolean run = false;
System.out.println("The factors of " + num + " are:");
System.out.print("1");
while (div <= Math.sqrt(num)) {
if (num % div == 0) {
System.out.print(" , "+div + " , " + num/div);
div++;
run = true;
} else {
div++;
}
}
System.out.print(" , "+num);
if (run == false) {
System.out.print("\nThis is a prime number!");
}
}
}
Test Cases
What is the number that you have chosen?
The factors of 10 are:
1 , 2 , 5 , 10
What is the number that you have chosen?
The factors of 5 are:
1 , 5
This is a prime number!
Hope this helps you out.

Why doesn't the scanner class recognize the other numbers?

public class Hello {
public static void main(String [] args){
int number, count = 0, sum = 0;
int Largest= 0, largestEvenNumber = 0;
Scanner console = new Scanner(System.in);
number = console.nextInt(); // read an integer entered by a user
if (number > Largest) { // Condition for computing the largest number
Largest = number;
}
if (number < 0) { // Condition for computing the number of negative integers in the sequence
count = count + 1;
}
if (number % 2 == 0) { // Condition for computing the largest even integer in the sequence
if (largestEvenNumber < number) {
largestEvenNumber = number;
}
}
if (number % 3 == 0) { // Condition for computing the sum of numbers divisible by 3
sum += number;
}
System.out.println("\nThe largest integer is " + Largest);
System.out.println("The number of negative integers in the sequence is " + count);
System.out.println("The largest even integer in the sequence is " + largestEvenNumber);
System.out.printf("The sum of numbers divisible by 3 is %d", sum);
}
}
I would like to get the expected output given below. But, the Scanner class is reading only the first number. How do I correct this without creating multiple objects?
Output:
2
-1
-5
-3
9
8
0
The largest integer is 2
The number of negative integers in the sequence is 0
The largest even integer in the sequence is 2
The sum of numbers divisible by 3 is 0
Process finished with exit code 0
expected Output:
The largest integer is 9
The number of negative integers in the sequence is 3
The largest even integer in the sequence is 8
The sum of numbers divisible by 3 is 6
Thank you!

You only call console.nextInt() once, so only one number is read. If you want to call you need to loop over calls to console.hasNext(). Since you're using System.in. E.g.:
while (console.hasNextInt()) {
number = console.nextInt();
// calculations
}

You are only reading input once. I don't see a loop in your code, so number = console.nextInt(); only runs once. What you should do is put it inside a loop, exit the loop when you have all the numbers (how you check that can be done in multiple ways), and while you're inside the loop put whatever input you receive into an array or another data structure. After you're done collecting input, do your checks over all the numbers on your data structure.

1- You must first receive the data from the user and then calculate it and generate the output. You can do this using the arrays and after finishing put your data, calculate on them.
for example :
private static final int DATA_SIZE = 5;
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
ArrayList<Integer> data = new ArrayList<>();
// put data in array
while (data.size() == DATA_SIZE){
data.add(scanner.nextInt());
}
// calculate data from array ...
}
2- When you call a field like nextInt() Scanner class , it is done only once, then you put it in a loop to be repeated several times ...
Of course, I have other suggestions for doing this
For example, you can use the array available in the main method (with knowledge, of course)
OR
First ask the user for the amount of data you have, then take it and then calculate
OR....

If you want to type all number at once ,you should set a terminal number. when you input all you number,you shoud add the terminal number to indicate input is over.
For example:
public static void main(String [] args){
int number, count = 0, sum = 0;
int Largest= 0, largestEvenNumber = 0;
Scanner console = new Scanner(System.in);
int endNumber = -1; //set the terminal number
do {
number = console.nextInt(); // read an integer entered by a user
if (number > Largest) { // Condition for computing the largest number
Largest = number;
}
if (number < 0) { // Condition for computing the number of negative integers in the sequence
count = count + 1;
}
if (number % 2 == 0) { // Condition for computing the largest even integer in the sequence
if (largestEvenNumber < number) {
largestEvenNumber = number;
}
}
if (number % 3 == 0) { // Condition for computing the sum of numbers divisible by 3
sum += number;
}
}while (number!=endNumber);
System.out.println("\nThe largest integer is " + Largest);
System.out.println("The number of negative integers in the sequence is " + count);
System.out.println("The largest even integer in the sequence is " + largestEvenNumber);
System.out.printf("The sum of numbers divisible by 3 is %d", sum);
}

The line if code is only being executed once. Thus, the Scanner is only taking in the first in put. Use a while loop to take in multiple inputs.

How to calculate prime fibonacci numbers?

(This is an extension from my previous question).
How to print a text notification beside prime fibonacci numbers?
Task:
The section of the assignment I am having difficulty with reads as follows:
Determine which of the first 20 Fibonacci numbers are prime numbers.
Put a “this is a prime” text notification in the printout from the Basic challenge.
Store the FibPrimes in an array called FibPrimes.
Problem:
I cannot seem to figure out how to take each individual fibonacci number, determine it is prime, put the prime fibonacci numbers in an array, and print the output. I was able to make a working program previously, but I didn't use code to calculate the primes, I manually entered them into an array (see previous attempt at bottom).
Attempt:
Here is what I have attempted:
The code that is relevant to this question is emphasized with comments.
package fibonaccinumbers;
public class FibonacciNumbers {
public static void main(String[] args) {
// Creation of Fibonacci Numbers Array.
// Let i represent the index number.
int [] FibNums = new int[20];
FibNums[0] = 0;
FibNums[1] = 1;
// Will add on each successive FibNums.
// Will be used to calculate average.
int FibSum = 1;
// RELEVANT TO QUESTION.
// Creation if Fibonacci Primes Array.
// Let n represent the index number.
int [] FibPrimes = new int[7];
int n=0;
// Printing first two fibonacci numbers.
System.out.println(0);
System.out.println(1 + "*");
// Printing remaining fibonacci numbers up to 20th term.
for (int i=2; i<FibNums.length;i++){ // Begin number generation loop.
FibNums[i] = FibNums[i-1] + FibNums[i-2];
// Checks if the fibonacci number is odd.
// A number is not odd if two divides into it evenly.
boolean oddcheck = true;
if (FibNums[i]%2==0){
oddcheck = false;
}
// RELEVANT TO QUESTION.
// A prime number can only be divided by 1 and inself.
// Divide FibNums[i] by every number inbetween.
// If a number divides evenly, it is not a prime (exception: 2).
// Else, the number is a prime.
boolean primecheck;
for (int divisor = 2; divisor < FibNums[i]/2; divisor++){
if (FibNums[i] % divisor == 0){
primecheck = false;
} else {
primecheck = true;
}
// REVELANT TO QUESTION.
// Add FibNums[i] to the FibPrimes[n] array if it is a prime.
if (primecheck == false){
FibPrimes[n] = FibNums[i];
n = n + 1;
}
// RELEVANT TO QUESTION.
// If any element in the FibPrimes array is equal to the FibNums
// array, then the number is a prime.
for (n=0; n<FibPrimes.length; n++){
if (FibNums[i] == FibPrimes[n]){
System.out.print("This is a prime." + " ");
}
}
// Prints odd fibonacci numbers with a star beside it.
// Prints even fibonacci numbers with no star beside it.
if (oddcheck == true){
System.out.println(FibNums[i] + "*");
} else {
System.out.println(FibNums[i]);
}
FibSum = FibSum + FibNums[i];
} // End number generation loop.
System.out.print ( "The average is" + " " + FibSum/20);
}
}
Output:
0
1*
The average is 0The average is 0The average is 0The average is 0This is a prime. 8
This is a prime. 8
The average is 013*
13*
13*
13*
The average is 321*
This is incorrect.
Previous Attempt:
This solution "worked", but in order to not take the "lazy route" I must do the calculations using code. Only relevant snippets are shown:
// Creation if Fibonacci Primes Array.
// Ideally, this should be caulculated.
int [] FibPrimes = new int[7];
FibPrimes[0] = 2;
FibPrimes[1] = 3;
FibPrimes[2] = 5;
FibPrimes[3] = 13;
FibPrimes[4] = 89;
FibPrimes[5] = 233;
FibPrimes[6] = 1597;
// If any element in the FibPrimes array is equal to the FibNums
// array, then the number is a prime.
for (int n=0; n<FibPrimes.length; n++){
if (FibNums[i] == FibPrimes[n]){
System.out.print("This is a prime." + " ");
}
}
Output:
0
1*
1*
This is a prime. 2
This is a prime. 3*
This is a prime. 5*
8
This is a prime. 13*
21*
34
55*
This is a prime. 89*
144
This is a prime. 233*
377*
610
987*
This is a prime. 1597*
2584
4181*
The average is 547
This is the desired output! However, I cannot use this because I must calculate the prime fibonacci numbers using code. This is the "lazy route".
Thank you.

Just 10 mins on google and you will be able to create something simple and fast.
Using the mathematical formulas below :
which you can find more one this paper you can make your prime fibonacci sequence. In addition you will need a way to check which numbers in the sequence are primes so a quick way is through AKS algorithm
Here is a full example of all the above :
public class FibonacciSequence {
public static void main(String[] args) {
for (int i = 1; i <= 20; i++) {
int num = (int) ((getY_1(i) - getY_2(i)) / Math.sqrt(5));
if (isPrime(num)) {
System.out.print("This is a prime : ");
}
System.out.println(num);
}
}
public static double getY_1(int N) {
return Math.pow((1 + Math.sqrt(5.0)) / 2.0, N);
}
public static double getY_2(int N) {
return Math.pow((1 - Math.sqrt(5.0)) / 2.0, N);
}
public static boolean isPrime(int num) {
if (num == 2 || num == 3)
return true;
if (num % 2 == 0 || num % 3 == 0) {
return false;
}
int i = 5;
int s = 2;
while (i * i <= num) {
if (num % i == 0) {
return false;
}
i += s;
s = 6 - s;
}
return true;
}
}
Of course you can exclude the value (1) if you don't feel like identifying it as a prime :P.
Output :
This is a prime : 1
This is a prime : 1
This is a prime : 2
This is a prime : 3
This is a prime : 5
8
This is a prime : 13
21
34
55
This is a prime : 89
144
This is a prime : 233
377
610
987
This is a prime : 1597
2584
4181
6765
P.S : I had free time :P

Testing primes in Java - adding additional conditions

Beginner here. So I want to write a program that prints out all the prime numbers up to the number the user entered. E.g., user enters 5, program prints out 2 and 3. That part I understand, however what I am struggling with, is what if I want the program to print out whether the number the user entered is a prime or not (simple yes or no) IF the entered number is bigger than, let's say, 50. Here is code for first part:
public class Primes {
public static void main(String args[]) {
System.out.println("All primes up to: ");
int num = new Scanner(System.in).nextInt();
System.out.println("Prime numbers from 1 to " + num + " are: ");
for(int number = 2; number<=num; number++){
if(isPrime(number)){
System.out.println(number);
}
}
}
public static boolean isPrime(int number){
for(int i=2; i<number; i++){
if(number%i == 0){
return false;
}
}
return true;
}
}
I honestly can't wrap my around as to what I should be doing next. My first program ever ("Hello world" does not count ;P).

Edit :
Your current code seems to work fine.
As per your doubt as mentioned in one of the comments : Yes, but where do I add if statement that does the following: if the number entered is below 50, then the program prints out all the prime numbers up to the entered number. If the number the user entered is bigger than 50, it tells only whether the entered number is prime or not ( simply "It's a prime" or "No, it's not a prime"). Hope that made things clearer
The check you need to put is after you take the input :
int num = new Scanner(System.in).nextInt();
if( number > 50 )
{
if(isPrime(number))
{
// print out is prime
}
// print out it is not prime
}
else
{
System.out.println("Prime numbers from 1 to " + num + " are: ");
for(int number = 2; number<=num; number++){
if(isPrime(number)){
System.out.println(number);
}
}
}
SUGESTIONS :
However, just to touch upon the algorithmic part, I would recommend using Sieve of Eratosthenes for picking out all the prime numbers within a given range, as you need in your case.
Example :
To find all the prime numbers less than or equal to 30, proceed as follows:
First generate a list of integers from 2 to 30:
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Strike (sift out) the multiples of 2 resulting in:
2 3 5 7 9 11 13 15 17 19 21 23 25 27 29
The first number in the list after 2 is 3; strike the multiples of 3 from the list to get:
2 3 5 7 11 13 17 19 23 25 29
The first number in the list after 3 is 5; strike the remaining multiples of 5 from the list:
2 3 5 7 11 13 17 19 23 29
The first number in the list after 5 is 7, but 7 squared is 49 which is greater than 30 so the process is finished. The final list consists of all the prime numbers less than or equal to 30.
Here's the code attached for reference ( Disclaimer : I'm picking up this code here from this site. Just pasted it here for more immediate visibility).
Code :
public class PrimeSieve {
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
// initially assume all integers are prime
boolean[] isPrime = new boolean[N + 1];
for (int i = 2; i <= N; i++) {
isPrime[i] = true;
}
// mark non-primes <= N using Sieve of Eratosthenes
for (int i = 2; i*i <= N; i++) {
// if i is prime, then mark multiples of i as nonprime
// suffices to consider mutiples i, i+1, ..., N/i
if (isPrime[i]) {
for (int j = i; i*j <= N; j++) {
isPrime[i*j] = false;
}
}
}
// count primes
int primes = 0;
for (int i = 2; i <= N; i++) {
if (isPrime[i]) primes++;
}
System.out.println("The number of primes <= " + N + " is " + primes);
}
}

Try this..
int j = 2; //variable
int result = 0; //variable
int number = 0; //variable
Scanner reader = new Scanner(System.in); //Scanner object
System.out.println("Please enter a number: "); //Instruction
number = reader.nextInt(); //Get the number entered
while (j <= number / 2) //start loop, during loop j will become each number between 2 and
{ //the entered number divided by 2
if (number % j == 0) //If their is no remainder from your number divided by j...
{
result = 1; //Then result is set to 1 as the number divides equally by another number, hergo
} //it is not a prime number
j++; //Increment j to the next number to test against the number you entered
}
if (result == 1) //check the result from the loop
{
System.out.println("Number: " + number + " is Not Prime."); //If result 1 then a prime
}
else
{
System.out.println("Number: " + number + " is Prime. "); //If result is not 1 it's not a prime
}
this is more efficient way tough:-
public boolean isPrime(int n) {
// fast even test.
if(n > 2 && (n & 1) == 0)
return false;
// only odd factors need to be tested up to n^0.5
for(int i = 3; i * i <= n; i += 2)
if (n % i == 0)
return false;
return true;
}

however what I am struggling with, is what if I want the program to print out whether the number the user entered is a prime or not (simple yes or no).
Your current isPrime function seems to work, so just ask for a number and test it.
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
if (isPrime(num)) {
System.out.printf("%d yes%n", num);
} else {
System.out.printf("%d no%n", num);
}
}
Or with a ternary,
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
System.out.printf("%d %s%n", num, isPrime(num) ? "yes" : "no");
}
Edit Based on your comment, move your print up sequence to a method
public static void primesUpTo(int num) {
System.out.println("Prime numbers from 1 to " + num + " are: ");
for (int number = 2; number <= num; number++) {
if (isPrime(number)) {
System.out.println(number);
}
}
}
Then
Scanner scanner = new Scanner(System.in);
while (scanner.hasNextInt()) {
System.out.println("Enter a number (is it prime): ");
int num = scanner.nextInt();
if (num > 50) {
System.out.printf("%d %s%n", num, isPrime(num) ? "yes" : "no");
} else {
primesUpTo(num); // <-- call the method above.
}
}

If i understand the question right:
If user enteres number lesser than or equal to 50, then print all primes that are lesser than that number.
Otherwise, just write if inputted number is a prime.
With already existing isPrime() method:
int num = new Scanner(System.in).nextInt();
if (num <= 50) {
System.out.println("Prime numbers from 1 to " + num + " are: ");
for (int number = 2; number <= num; number++) {
if (isPrime(number)) {
System.out.println(number);
}
}
} else { //num > 50
if(isPrime(num)) {
System.out.println(num + " is prime.");
} else {
System.out.println(num + " isn't prime.");
}
}

How to check if number is divisible by a certain number?

I am using AndEngine to add sprites to the screen and come across using the movemodifier method.
I have two integers
MaxDuration and MinDuration;
What i want to do is when the user gets to a score of a certain increment.
Like for example.. when the user gets to 20(the integer changes) when the user gets to 40(the integer changes). So basically count by 20 and every time the score meets a number divisible by 20 the integer's change. I hope this makes sense.
Is there any method or way to do this? I have an UpdateTime handler that can check the score just about every second.
Any ideas?

n % x == 0
Means that n can be divided by x. So... for instance, in your case:
boolean isDivisibleBy20 = number % 20 == 0;
Also, if you want to check whether a number is even or odd (whether it is divisible by 2 or not), you can use a bitwise operator:
boolean even = (number & 1) == 0;
boolean odd = (number & 1) != 0;

package lecture3;
import java.util.Scanner;
public class divisibleBy2and5 {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println("Enter an integer number:");
Scanner input = new Scanner(System.in);
int x;
x = input.nextInt();
if (x % 2==0){
System.out.println("The integer number you entered is divisible by 2");
}
else{
System.out.println("The integer number you entered is not divisible by 2");
if(x % 5==0){
System.out.println("The integer number you entered is divisible by 5");
}
else{
System.out.println("The interger number you entered is not divisible by 5");
}
}
}
}