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How to find factorial and show result of counting in console?

public class Car {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
System.out.println(n+"!="+factorial(n));
}
public static int factorial(int num) {
return (num == 0) ? 1 : num * factorial (num - 1);
}
}
how make this code to text in console 3! = 1*2*3 = 6?

Don't use recursion for this. Besides, it isn't really efficient or necessary.
Scanner in = new Scanner(System.in);
int n = in.nextInt();
int fact = 1;
String s = n + "! = 1";
for (int i = 2; i <= n; i++) {
fact *= i;
s += "*" + i;
}
s += " = ";
System.out.println(s + fact);

There can be many ways to do it e.g. you can build the required string or print the trail while calculating the factorial. In the following example, I have done the former.
As an aside, you should check the input whether it is a positive integer.
import java.util.Scanner;
public class Car {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("Enter a positive integer: ");
int n = in.nextInt();
if (n >= 0) {
StringBuilder strFact = new StringBuilder();
int fact = factorial(n, strFact);
if (strFact.length() > 0) {
// Delete the last '*'
strFact.deleteCharAt(strFact.length() - 1);
System.out.println(n + "!= " + strFact + " = " + fact);
} else {
System.out.println(n + "!= " + fact);
}
} else {
System.out.println("This is an invalid input.");
}
}
public static int factorial(int num, StringBuilder strFact) {
int fact;
if (num == 0) {
fact = 1;
} else {
fact = num * factorial(num - 1, strFact);
strFact.append(num + "*");
}
return fact;
}
}
A sample run:
Enter an integer: 3
3!= 1*2*3 = 6

How to modify this code to print the 3 integers in order?

I have a code that prints the biggest integer between 3 integers and I want to sort these 3 integers (like num < num1 < num2).
I want to modify my code to achieve this, how can I do it?
import java.util.Scanner;
public class digits {
public static void main(String[] args) {
int num = 0;
int num1 = 0;
int num2 = 0;
int big = 0;
System.out.println("Please insert 3 numbers: ");
Scanner number = new Scanner(System.in);
if (number.hasNextInt()) {
num = number.nextInt();
big = num;
}
if (number.hasNextInt()) {
num1 = number.nextInt();
if (num1 > num) {
big = num1;
}
}
if (number.hasNextInt()) {
num2 = number.nextInt();
if (num2 > num && num2 > num1) {
big = num2;
}
System.out.println(big + ">" + num1 + ">" + num);
} else {
System.out.println("Error: Invalid Value.");
}
}
}

Try below code
public static void main(String[] args) {
System.out.println("Please insert 3 numbers: ");
Scanner number = new Scanner(System.in);
Integer[] input = new Integer[3];
int i = 0;
while (i != 3) {
input[i++] = number.nextInt();
}
number.close();
Arrays.sort(input, Collections.reverseOrder());
StringBuffer sb = new StringBuffer();
for (Integer a : input) {
sb.append(a).append(">");
}
System.out.println(sb.substring(0, sb.length() - 1));
}

if(num1>num)
{
big=num1;
}
Change this to:
if(num1>num)
{
big=num1;
}
else
{
// swap num1 and num
int tmp = num;
num = num1;
num1 = num;
}
Also change
if(num2>num && num2>num1)
{
big=num2;
}
to
if(num2>num1)
{
big=num2;
}
else
{
// num1 is largest, so swap num1 and num2
int tmp = num1;
num1 = num2;
num2 = tmp;
if(num > num1){
//swap num and num1
int t = num1;
num1 = num;
num = t;
}
}

Look at your code: you're choosing the biggest of the three numbers (big), but you never change num1 or num.
So, your result will always be: greater number>second value from System.in>third value from System.in.
In other words, you're sorting only the higher value.

Something like this should work
import java.util.Scanner;
public class digits {
public static void main(String[] args)
{
int[] nums = new int[3];
int k = 0;
System.out.println("Please insert 3 numbers: ");
Scanner number = new Scanner (System.in);
while (number.hasNext() && k < 3) {
int i = 0;
try {
i = Integer.parseInt(number.nextLine());
}
catch (NumberFormatException e) {
System.out.println("Error: Invalid Value.");
}
nums[k] = i;
k++;
}
Arrays.sort(nums);
System.out.println(nums[2]+ ">" +nums[1]+ ">" +nums[0]);
}
}

Binary to Decimal Java converter

I am creating a code that allows you to convert a binary number to a decimal number and vice versa. I have created a code that converts decimal to binary but can not workout how to implement the binary to decimal aspect.
My code for decimal to binary is below:
import java.util.*;
public class decimalToBinaryTest
{
public static void main (String [] args)
{
int n;
Scanner in = new Scanner(System.in);
System.out.println("Enter a positive interger");
n=in.nextInt();
if(n < 0)
{
System.out.println("Not a positive interger");
}
else
{
System.out.print("Convert to binary is: ");
binaryform(n);
}
}
private static Object binaryform(int number)
{
int remainder;
if(number <= 1)
{
System.out.print(number);
return " ";
}
remainder= number % 2;
binaryform(number >> 1);
System.out.print(remainder);
{
return " ";
}
}
}
An explanation to how the binary to decimal code work would help as well.
I have tried the method of the least significant digit*1 then the next least *1*2 then *1*2*2 but can not get it to work.
Thank you #korhner I used your number system with arrays and if statements.
This is my working code:
import java.util.*;
public class binaryToDecimalConvertor
{
public static void main (String [] args)
{
int [] positionNumsArr= {1,2,4,8,16,32,64,128};
int[] numberSplit = new int [8];
Scanner scanNum = new Scanner(System.in);
int count1=0;
int decimalValue=0;
System.out.println("Please enter a positive binary number.(Only 1s and 0s)");
int number = scanNum.nextInt();
while (number > 0)
{
numberSplit[count1]=( number % 10);
if(numberSplit[count1]!=1 && numberSplit[count1] !=0)
{
System.out.println("Was not made of only \"1\" or \"0\" The program will now restart");
main(null);
}
count1++;
number = number / 10;
}
for(int count2 = 0;count2<8;count2++)
{
if(numberSplit[count2]==1)
{
decimalValue=decimalValue+positionNumsArr[count2];
}
}
System.out.print(decimalValue);
}
}

sample:
00000100
0 - 1
0 - 2
1 - 4
0 - 8
0 - 16
0 - 32
0 - 64
0 - 128
Sum values with bit 1 = 4
Good luck!

int decimal = Integer.parseInt("101101101010111", 2);
or if you prefer to doit your self
double output=0;
for(int i=0;i<str.length();i++){
if(str.charAt(i)== '1')
output=output + Math.pow(2,str.length()-1-i);
}

Here is a program which does that.
Make sure the integers you give to int and not too large.
import java.util.Scanner;
public class DecimalBinaryProgram {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
while (true){
System.out.println("Enter integer in decimal form (or # to quit):");
String s1 = in.nextLine();
if ("#".equalsIgnoreCase(s1.trim())){
break;
}
System.out.println(decimalToBinary(s1));
System.out.println("Enter integer in binary form (or # to quit):");
String s2 = in.nextLine();
if ("#".equalsIgnoreCase(s2.trim())){
break;
}
System.out.println(binaryToDecimal(s2));
}
}
private static String decimalToBinary(String s){
int n = Integer.parseInt(s, 10);
StringBuilder sb = new StringBuilder();
if (n==0) return "0";
int d = 0;
while (n > 0){
d = n % 2;
n /= 2;
sb.append(d);
}
sb = sb.reverse();
return sb.toString();
}
private static String binaryToDecimal(String s){
int degree = 1;
int n = 0;
for (int k=s.length()-1; k>=0; k--){
n += degree * (s.charAt(k) - '0');
degree *= 2;
}
return n + "";
}
}
Of course for this method binaryToDecimal you can just do:
private static String binaryToDecimal(String s){
int n = Integer.parseInt(s, 2);
return n + "";
}
but I wanted to illustrate how you can do that explicitly.

do you want this?
private double dec(String s, int i) {
if (s.length() == 1) return s.equals("1") ? Math.pow(2, i) : 0;
else return (s.equals("1") ? Math.pow(2, i) : 0) + dec(s.substring(0, s.length() - 1), i - 1);
}
dec("101011101",0);

This is a version of a binary to decimal converter. I have used plenty of comments also. Just taught I would like to share it. Hope it is of some use to somebody.
import java.util.Scanner;
public class BinaryToDecimal
{
public static void main(String args[])
{
Scanner input = new Scanner(System.in);
System.out.println("Enter a binary number: ");
String binary = input.nextLine(); // store input from user
int[] powers = new int[16]; // contains powers of 2
int powersIndex = 0; // keep track of the index
int decimal = 0; // will contain decimals
boolean isCorrect = true; // flag if incorrect input
// populate the powers array with powers of 2
for(int i = 0; i < powers.length; i++)
powers[i] = (int) Math.pow(2, i);
for(int i = binary.length() - 1; i >= 0; i--)
{
// if 1 add to decimal to calculate
if(binary.charAt(i) == '1')
decimal = decimal + powers[powersIndex]; // calc the decimal
else if(binary.charAt(i) != '0' & binary.charAt(i) != '1')
{
isCorrect = false; // flag the wrong input
break; // break from loop due to wrong input
} // else if
// keeps track of which power we are on
powersIndex++; // counts from zero up to combat the loop counting down to zero
} // for
if(isCorrect) // print decimal output
System.out.println(binary + " converted to base 10 is: " + decimal);
else // print incorrect input message
System.out.println("Wrong input! It is binary... 0 and 1's like.....!");
} // main
} // BinaryToDecimal

I've written a converter that accepts both strings and ints.
public class Main {
public static void main(String[] args) {
int binInt = 10110111;
String binString = "10110111";
BinaryConverter convertedInt = new BinaryConverter(binInt);
BinaryConverter convertedString = new BinaryConverter(binString);
System.out.println("Binary as an int, to decimal: " + convertedInt.getDecimal());
System.out.println("Binary as a string, to decimal: " + convertedString.getDecimal());
}
}
public class BinaryConverter {
private final int base = 2;
private int binaryInt;
private String binaryString;
private int convertedBinaryInt;
public BinaryConverter(int b) {
binaryInt = b;
convertedBinaryInt = Integer.parseInt(Integer.toString(binaryInt), base);
}
public BinaryConverter(String s) {
binaryString = s;
convertedBinaryInt = Integer.parseInt(binaryString, base);
}
public int getDecimal() {
return convertedBinaryInt;
}
}

public static void main(String[] args)
{
System.out.print("Enter a binary number: ");
Scanner input = new Scanner(System.in);
long num = input.nextLong();
long reverseNum = 0;
int decimal = 0;
int i = 0;
while (num != 0)
{
reverseNum = reverseNum * 10;
reverseNum = num % 10;
decimal = (int) (reverseNum * Math.pow(2, i)) + decimal;
num = num / 10;
i++;
}
System.out.println(decimal);
}

Amicable numbers Java program

So I am having this strange output in which only the first number is checked twice while the second number is not even considered.Please help.
Code :-
import java.util.Scanner;
public class Amicable
{
private static int a,b;
private static String m,n;
public static void main()
{
acceptNumbers();
if (firstNumber() == secondNumber())
{
System.out.println(a+" and "+b+" are amicable numbers");
}
else System.out.println(a+" and "+b+" are not amicable numbers");
}
public static void acceptNumbers()
{
Scanner sc = new Scanner(System.in);
int count=0;
System.out.print("Enter two numbers [ separated by a ',' ] : ");
String input = sc.nextLine();
System.out.println();
for (int i = 0; i < input.length(); i++)
{
char c = input.charAt(i);
if (c == ',')
{
count++;
if (count == 1)
{
m = input.substring(0,i);
n = input.substring(0,i);
}
break;
}
}
if (count == 0)
{
System.out.println("Invalid operation : You have entered only 1 number");
}
m = m.trim(); n = n.trim();
a = Integer.valueOf(m);
b = Integer.valueOf(n);
}
public static int firstNumber()
{
int a1,a2=0;
for (int i = 0; i < m.length()-1; i++)
{
a1 = Integer.valueOf(m.charAt(i));
if (a%a1 == 0) a2 = a2+a1;
}
return a2;
}
public static int secondNumber()
{
int b1,b2=0;
for (int i = 0; i < n.length()-1; i++)
{
b1 = Integer.valueOf(n.charAt(i));
if (b%b1 == 0) b2 = b2+b1;
}
return b2;
}
}
And here is the output :-
Enter 2 numbers [ separated by a ',' ] : 248 , 222
248 and 248 are amicable numbers

your m and n are equal, because you have:
m = input.substring(0,i);
n = input.substring(0,i);
change it to:
m = input.substring(0,i);
n = input.substring(i+1);
Btw you are doing a lot of unnecessary stuff, complete solution (I don't care about exceptions):
import java.util.Scanner;
public class Amicable {
public static void main(String args[]) {
try {
Scanner sc = new Scanner(System.in);
System.out.print("Enter two numbers [ separated by a ',' ] : ");
String input = sc.nextLine();
String[] numbers = input.split(",");
int num1 = Integer.parseInt(numbers[0].trim());
int num2 = Integer.parseInt(numbers[1].trim());
int sum1 = 0, sum2 = 0;
for (int i = 1; i <= num1; i++) {
if (num1 % i == 0)
sum1 += i;
}
for (int i = 1; i <= num2; i++) {
if (num2 % i == 0)
sum2 += i;
}
if (sum1 == sum2)
System.out.println(num1 + " and " + num2
+ " are amicable numbers");
else
System.out.println(num1 + " and " + num2
+ " are not amicable numbers");
} catch (Exception e) {
e.printStackTrace();
}
}
}
parts of code from: http://www.daniweb.com/software-development/java/code/304600/amicable-numbers

a and b are derived from m and n, and the latter are initialized to exactly the same value:
m = input.substring(0,i);
n = input.substring(0,i);
Did you mean to set n to
n = input.substring(i+1);
?

m = input.substring(0,i);
n = input.substring(0,i);
m and n are having the same value.
n should be:
n = input.substring(i+1);
And now the second number will be assigned to n.

Need to output all prime numbers [duplicate]

This question already has answers here:
Java Display the Prime Factorization of a number
(7 answers)
Closed 9 years ago.
for the example 60 the answer should be 2 2 3 5 but it only comes up with 2 3 5.
import java.util.Scanner;
public class PrimeFactor {
public static void main(String[] args) {
System.out.print("Enter a positive number: ");
Scanner scanner = new Scanner (System.in);
int number = scanner.nextInt();
int count;
for (int i = 2; i<=(number); i++) {
count = 0;
while (number % i == 0) {
number /= i;
count++;
}
if (count == 0) {
continue;
}
System.out.print(i + " ");
}
}
}

The problem is that once it finds that 60 is divisible by 2, it keeps dividing it by 2 (in this case twice).
place the final bracket of the while statement AFTER the System.out.print and it works:
public static void main(String[] args) {
System.out.print("Enter a positive number: ");
Scanner scanner = new Scanner (System.in);
int number = scanner.nextInt();
int count;
for (int i = 2; i<=(number); i++) {
count = 0;
while (number % i == 0) {
number /= i;
count++;
if (count == 0) {
continue;
}
System.out.print(i + " ");
}
}
}

If you'd like a different way to do it:
import java.util.*;
import java.lang.*;
class Main
{
public static void main (String[] args) throws java.lang.Exception
{
System.out.print("Enter a positive number: ");
Scanner scanner = new Scanner (System.in);
int number = scanner.nextInt();
int divisor = 2;
while(number != 1) {
if(number % divisor == 0) {
System.out.println(divisor + " ");
number /= divisor;
}
else {
divisor++;
}
}
}
}