I'm trying to make a simple program that will display 20 random numbers between 1 and 100 and then print out which numbers are divisible by 3 and equivalent to 1%3 and 2%3. It seems to work just fine but I've noticed it only works with the very last number in the list. What am I missing to include all the numbers in the search for my math? Thank you in advance for any help I can get!
import java.util.Random;
public class Lab5 {
public static void main(String[] args) {
Random rnd = new Random();
int repeat = 19;
int n = 0;
for(int i=0;i<=repeat;i++){
n = rnd.nextInt(100)+1;
System.out.print(n+", ");
}
System.out.println();
System.out.println("-------------------------------------");
if(n % 3 == 0){
System.out.println("Numbers divisible by three: "+n+(", "));
}else{
System.out.println("Numbers divisible by three: NONE");
}
System.out.println("-------------------------------------");
if(n == 1 % 3){
System.out.println("Numbers equivalent to one modulo three: "+n+(", "));
}else{
System.out.println("Numbers equivalent to one modulo three: NONE");
}
System.out.println("-------------------------------------");
if(n == 2 % 3){
System.out.println("Numbers equivalent to two modulo three: "+n+(", "));
}else{
System.out.println("Numbers equivalent to two modulo three: NONE");
}
}
}
It is only printing the last number because the check if the number is divisible, etc is not in your for loop at the top. Simply copy and paste all of the code below it into your for loop and it should work as you intended.
You also have an error here: if (n == 1 % 3), it is legal but will check if n is equal to the remainder of 1 / 3. I don't think that is what you wanted to achieve, so correct it like this: if (n % 3 == 1) as Ypnypn suggested.
Your n is declared outside of the loop body, so its value will persist. However, since you are overwriting n in each loop iteration, only the last value of n will persist and will be used by other parts of the program.
As Ypnypn has said, correct your use of modulo, and as Arbiter and deanosaur have suggested, move the rest of the program logic inside the for loop
The correct syntax for modulus is n % 3 == 2. The current code n == 2 % 3 means n == 0, since the order of operations in Java requires that modulus is evaluated before equality.
You are putting all the output statements (System.out.println()) outside your loop, so it only outputs the last value.
Move your output statements so they are inside your loop:
public static void main(String[] args) {
Random rnd = new Random();
int repeat = 19;
int n = 0;
int[] numbers = new int[3]; // To hold how many numbers have modulo 0, 1 or 2
for(int i = 0; i <= repeat; i++) {
n = rnd.nextInt(100)+1;
System.out.print(n+", ");
if(n % 3 == 0)
System.out.println("The number " + n + " is divisible by 3");
else
System.out.println("" + n + " modulo 3 = " + n % 3);
numbers[n % 3]++;
}
System.out.println("Numbers divisible by 3: " + numbers[0]);
System.out.println("Numbers with modulo 3 = 1: " + numbers[1]);
System.out.println("Numbers with modulo 3 = 2: " + numbers[2]);
}
Well .. you did not calculate anything in the loop, so your print statements work the last value of n after you exited the loop. Try something like
package com.example.modulo;
import java.util.Random;
public class Modulo {
public static void main(String[] args) {
Random rnd = new Random();
int repeat = 19;
int n = 0;
int[] nMod = new int[3];
nMod[0] = 0;
nMod[1] = 0;
nMod[2] = 0;
for (int i = 0; i <= repeat; i++) {
n = rnd.nextInt(100) + 1;
nMod[n%3] = nMod[n%3] + 1;
System.out.print(n + " (" + n%3 + "), ");
}
System.out.println();
System.out.println("-------------------------------------");
System.out.println("Numbers divisible by three: " + nMod[0] + (", "));
System.out.println("Numbers equivalent to one modulo three: " + nMod[1] + (", "));
System.out.println("Numbers equivalent to two modulo three: " + nMod[2] + (", "));
}
}
Related
I'm solving a problem to find all the multiples of 3 and 5 within a number that is inputted from the user.
I want to show all the multiples and their sum to the user.
I can't find a way to add the values to the array containing the multiples.
Here is the code:
import java.util.Arrays;
import java.util.Scanner;
import java.util.stream.*;
public class application {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
// Input the number from user:
System.out.println("Enter a number to calculate the sum of all the multiples of 3 or 5 below it: ");
int number = input.nextInt();
int i = 1;
int[] arr = {};
System.out.println("The multiples of 3 and 5 below the number " + number + " are: ");
while(i < number) {
if (i % 3 == 0 || i % 5 == 0 ) {
System.out.print(i + ",");
arr = Arrays.copyOf(arr, arr.length + 1);
arr[arr.length - 1] = i;
}
i++;
}
int sum = IntStream.of(arr).sum();
System.out.println("The sum of these multiples is: " + sum);
//Thank you :D
}
}
Try just adding the multiples together as they are found.
You do not need an array to store them since your code is a) printing out the multiple found and then b) printing out the sum of the multiples
instead of array you can direct sum of the multiple 3 and 5
int sum = 0
inside if statement
if (i % 3 == 0 || i % 5 == 0 ) {
System.out.print(i + ",");
sum += i;
//arr = Arrays.copyOf(arr, arr.length + 1);
//arr[arr.length - 1] = i;
}
and print out the sum
I'm trying to write a java code that displays the prime factorization of a number in two forms: multiplied out and multiplied out with exponents. For example, the proper output would look like this:
Enter a number
100
The prime factorization of 100 is:
100 = 2 * 2 * 5 * 5
100 = 2^2 * 5^5
Except my current code only outputs this:
Enter a number
100
The prime factorization of 100 is:
100 = 2 2 5 5
Here's what my code looks like:
import java.util.Scanner;
public class Factorization {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
// user inputs variables here
System.out.println("Enter a number");
long n = keyboard.nextLong();
System.out.println("The prime factorization of " + n + " is: ");
System.out.print(n+" = ");
// solution for 1 as an input
if(n==1){
System.out.println("1");
}
// for each potential factor
for (long factor = 2; factor*factor <= n; factor++) {
// if factor is a factor of n, repeatedly divide it out
while (n % factor == 0) {
System.out.print(factor + " ");
n = n / factor;
}
}
// if biggest factor occurs only once, n > 1
if (n > 1){
System.out.println(n);
} else {
System.out.println();
}
}
}
How can I make it give the proper output?
Thank you so much!
Printing out the first form is easy, and would just require a slight modification to your code so that it would print out the *. The second form, however, is a bit more tricky as you can't just directly print out the factors as you obtain them, since you need to count how many times each one occurs to know their exponent. There are a few different ways you could do this, but I thought the simplest would be to use 2 ArrayLists. One of these ArrayLists would contain the bases, while the other would contain the exponents for each base. This is my implementation, and I added some comments for clarification.
import java.util.Scanner;
import java.util.ArrayList;
public class Factorization{
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
// user inputs variables here
System.out.println("Enter a number");
long n = keyboard.nextLong();
long m = n;
System.out.println("The prime factorization of " + n + " is: ");
System.out.print(n+" = ");
ArrayList<Long> bases = new ArrayList<Long>(); //ArrayList containing each unique factor
ArrayList<Long> exponents = new ArrayList<Long>(); //ArrayList containing exponents, or the amount of times that factor is multiplied
// solution for 1 as an input
if(n==1){
System.out.println("1");
}
// for each potential factor
for (long factor = 2; factor*factor <= n; factor++) {
// if factor is a factor of n, repeatedly divide it out
while (n % factor == 0) {
n = n / factor;
if (!bases.contains(factor)){ //if the factor is not already in the bases list, it's unique and should be added
bases.add(factor);
exponents.add(1L);
}
else{ //if the factor is already in the bases list, increment its exponent by 1
exponents.set(bases.indexOf(factor), exponents.get(bases.indexOf(factor)) + 1);
}
}
}
// if biggest factor occurs only once, n > 1
if (n > 1){
if (!bases.contains(n)){
bases.add(n);
exponents.add(1L);
}
else{
exponents.set(bases.indexOf(n), exponents.get(bases.indexOf(n)) + 1);
}
}
//printing out the first form
for (int i = 0; i < bases.size(); i++)
{
for (int j = 0; j < exponents.get(i); j++) //each base is printed out an amount of times equal to its exponent
{
if (i != 0 || j != 0) //making sure we don't print * before the first base
{
System.out.print(" * ");
}
System.out.print(bases.get(i));
}
}
System.out.println();
System.out.print(m+" = ");
//printing out the second form
for (int i = 0; i < bases.size(); i++)
{
if (i >= 1) //making sure we don't print * before the first base
{
System.out.print(" * ");
}
System.out.print(bases.get(i) + "^" + exponents.get(i));
}
}
}
If you want to learn more about ArrayLists, I recommend you check out the official Java documentation on it here: https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html.
I hope this helps.
I'm a Java beginner, please bear with me. :) I haven't learned anything like if statements and such yet, I've only learned about loops, variables, and classes. I need to write a single loop which produces the following output:
10 0 9 1 8 2 7 3 6 4 5 5
I can see from the segment, that the difference between the numbers is reduced by one, so from 10 to 0 it is subtracted 10, then from 0 to 9 it is added by 9, and it goes on alternating between adding and subtracting.
My idea was to create the loop where my variable i = 10 decreases by 1 in the loop (i--) but I'm not quite sure how to alternate between adding and subtracting in the loop?
public class Exercise7 {
public static void main(String[] args) {
for(int i = 10; i >= 0; i--) {
System.out.print(i + " ");
}
}
}
Why not have two extra variables and the increment one and decremented the other:
int y = 0;
int z = 10;
for(int i = 10; i >= 5; i--) {
System.out.print(z + " " + y + " ");
y++;
z--;
}
Output:
10 0 9 1 8 2 7 3 6 4 5 5
However we can also do this without extra variables:
for(int i = 10; i >= 5; i--) {
System.out.print(i + " " + 10-i + " ");
}
I don't think the OP actually wanted somebody to do their homework for them, so I'm gonna stick to answering the question they actually asked: how to alternate between two operations within a loop (so they can keep the algorithm they came up with :)).
There's a nifty "trick" that's very often used when we want to do something every other iteration in most programming languages. You'll most definitely come across it in your life, and it could be perplexing if you've got no clue what's going on, so here it goes!
The modulo (%) operator will yield the remainder of the division between its operands.
For instance, consider the following: 7 ÷ 2 = 3.5
When working for integers, you'd say that 7 ÷ 2 = 3, then you're left with 1.
In this case, when all variables are ints, in Java, 7 / 2 would be 3 and 7 % 2 is 1.
That's modulo for you!
What's interesting about this operator is inherent to what's interesting about division in general, and one case in particular: the remainder of a division by 2 is always either 0 or 1... and it alternates! That's the key word here.
Here comes the "trick" (not really a trick, it's basically a pattern considering how widely used it is) to alternating operations over iterations:
take any variable that is incremented every iteration in a loop
test for the remainder of the division of that variable by 2
if it's 0, do something, otherwise (it'll be 1), take the alternate path!
In your case, to answer your actual question (although others do have good points, I"m not trying to take that away from anybody), you could consider using something like that:
if( i % 2 == 0 ) {
// i is even, subtract
} else {
// i is odd, add
}
That'd allow you to keep going with the algorithm you initially thought of!
public class exercise7 {
public static void main(String[] args) {
for(int i = 10; i >= 5; i--) {
System.out.print(i + " " + (10-i) + " ");
}
}
}
Or you can do it this way, if you want to be a wiseass ;)
for(int i = 0, arr[] = {10,0,9,1,8,2,7,3,6,4,5,5}; i < arr.length; i++) {
System.out.print(arr[i] + " ");
}
This looks a bit like a homework assignment, so I won't give you working code.
But remember that you can put multiple print statements inside the for loop. You don't necessarily have to iterate 10 times to get your output. 5 times is totally enough. And as already stated in a comment above: the numbers alternate between i and 10-i, for the right range of i.
replace i >= 0 with i >= 5
add this : System.out.print((10-i--) + " ");
starting from what you did
public class Exercise7 {
public static void main(String[] args) {
for(int i = 10; i >= 5; ) {
System.out.print(i + " " + (10-i--) + " ");
}
}
}
Somethings don't need overthinking:
public class Answer2 {
public static void main(String[] args) {
for (int i = 0; i <= 5; i++){
System.out.println(i);
System.out.println(10 - i);
}
}
}
edit
You CAN and should generalize your task. Here is an example how you could do it (I won't write the method, since it's your job - instead I'll alter my answer just to show you the possibilities)
public class Answer2 {
private static final Random RANDOM = new Random();
public static void main(String[] args) {
//You can use any upper bound for 'someLength'
int someLength = 1 + RANDOM.nextInt(20);
for (int i = 0; i <= someLength / 2; i++) {
System.out.println(someLength - i);
System.out.println(i);
}
}
}
Who said that you can only use one System.out.print in the loop?
for (int i=0; i < 5; i++) {
System.out.print((10 - i) + " " + (i + 1) + " ");
}
You should think about generalizing the series. As you have observed, the series alternates between addition and subtraction. Also, the difference goes down by one at each step. You can define variables for these two and adjust them in the loop.
public static void main(String[] args) {
int term = 10;
int sign = 1;
for(int delta = 10; delta >= -1; delta--) {
System.out.print(term + " ");
sign = -1 * sign;
term = term + sign * delta;
}
}
Simply run a loop either starting from 0 or starting from 10.
1.
If you start from 10
for(int i=10;i>=5;i--){
System.out.print(i + " " + (10-i) + " ");
}
2.
If you start from 0
for(int i=0;i<=5;i++){
System.out.print((10-i) + " " + i + " ");
}
The output will be:
10 0 9 1 8 2 7 3 6 4 5 5
I tried this code. It worked for me.
for(int i = 10; i >= 5; i--) {
System.out.print(i + " ");
System.out.print(10-i + " ");
}
This is here. The output list is a list of combinations to make 10;
10 0 9 1 8 2 7 3 6 4 5 5
10 + 0 = 10
9 + 1 = 10
8 + 2 = 10
7 + 3 = 10
6 + 4 = 10
5 + 5 = 10
int n = 10;
int half = n / 2;
if(n % 2 == 1){
half++;
}
for(int x = n; x >= half;x--){
int remainder = n % x;
if(remainder == 0){
remainder = n - x;
}
System.out.print(x);
System.out.print(" ");
System.out.println(remainder);
}
so for class I'm supposed to make a guessing game that gives you clues as you get closer to the answer. My question is when i run it and i get one Number correct, I would obviously keep that number and keep going with the other 4 numbers, when I do that, the problem is my correct digits counter keeps rising even if I don't get other digits correct.. how would I remedy this? Would i be able to add breaks in each of the if statements or would that completely exit me out of my do while loop?
public class GuessingGame {
public static void main(String[] args) {
int guess,numDigitsCorrect=0,sumDigitsCorrect=0,attempts=0,answer;
Random rng = new Random();
Scanner consoleScanner = new Scanner(System.in);
answer = rng.nextInt(90000) + 10000;
System.out.println("I have randomly chosen a 5-digit code for you to guess.Each time you guess,\n"
+ "I will tell you how many digits are correct and the sum of the digits that are correct."
+ "For example, if the number is \"68420\" and you guess 12468, I will respond:\n"
+ "Number of Digits Correct: 1\n"
+ "Sum of Digits Correct: 4\n"
+ "From deduction, you will know the 4 was correct in the guess."
+ "\nNow its your turn..................................................................");
do{
System.out.print("Please enter a 5-digit code (your guess): ");
guess = consoleScanner.nextInt();
int g1 = guess/10000;
int g2 = guess%10000/1000;
int g3 = guess % 10000 % 1000 / 100;
int g4 = guess % 10000 % 100 /10;
int g5 = guess % 10000 % 10 / 1;
int a1 = answer/10000;
int a2 = answer%10000/1000;
int a3 = answer % 10000 % 1000 / 100;
int a4 = answer % 10000 / 100 / 10;
int a5 = answer % 10000 % 10 / 10;
if(g1 == a1)
{
numDigitsCorrect ++;
sumDigitsCorrect += a1;
System.out.println("\nNumber of digits correct: " + numDigitsCorrect) ;
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
System.out.println();
}
if(g2 == a2)
{
numDigitsCorrect ++;
sumDigitsCorrect += a2;
System.out.println("Number of digits correct: " + numDigitsCorrect) ;
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
System.out.println();
}
if (g3 == a3)
{
numDigitsCorrect ++;
sumDigitsCorrect += a3;
System.out.println("Number of digits correct: " + numDigitsCorrect) ;
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
System.out.println();
}
if (g4 == a4)
{
numDigitsCorrect ++;
sumDigitsCorrect += a4;
System.out.println("Number of digits correct: " + numDigitsCorrect) ;
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
System.out.println();
}
if (g5 == a5)
{
numDigitsCorrect ++;
sumDigitsCorrect += a5;
System.out.println("Number of digits correct: " + numDigitsCorrect) ;
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
System.out.println();
}
if(guess == answer)
{
System.out.println("****HOORAY! You solved it. You are so smart****");
break;
}
}while (guess != answer);
}
}
Few things to fix -
Make sure your a4, a5 are correct
int a4 = answer % 10000 % 100 / 10; // note the modulus
int a5 = answer % 10000 % 10; // note divided by 1 or remove the redundant statement
Move your print statement out of your if block to the end of all if inside the do block as -
if (g1 == a1) {
numDigitsCorrect++;
sumDigitsCorrect += a1;
}
... //other if statements
if (guess == answer) {
System.out.println("****HOORAY! You solved it. You are so smart****");
break;
}
System.out.println("Number of digits correct: " + numDigitsCorrect);
System.out.println("Sum of digits correct: " + sumDigitsCorrect);
Also since you already do a check
if (guess == answer) {
System.out.println("****HOORAY! You solved it. You are so smart****");
break;
}
within your do you can change your while condition to true as -
do {
... your existing code
} while(true);
To answer
Would i be able to add breaks in each of the if statements
If you do so, for even a single digit match your loop will exit(break).
Importantly to fix the counter, initialize the counter within the do block as
do {
numDigitsCorrect = 0;
sumDigitsCorrect = 0;
.. // existing logic
}
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.");
}
}