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How to get the last number of an integer input

Binary to decimal converter without the use of built-in Java methods. It must do this conversion automatically. When I get the last number of the integer during input it gives me a number format exception.
import java.util.Scanner;
public class Homework02 {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter an 8-bit binary number:");
int binary = keyboard.nextInt();
int copyBinary = binary;
int firstDigit = Integer.parseInt(Integer.toString(copyBinary).substring(0, 1));
int secondDigit = Integer.parseInt(Integer.toString(copyBinary).substring(1, 2));
int thirdDigit = Integer.parseInt(Integer.toString(copyBinary).substring(2, 3));
int fourthDigit = Integer.parseInt(Integer.toString(copyBinary).substring(3, 4));
int fifthDigit = Integer.parseInt(Integer.toString(copyBinary).substring(4, 5));
int sixthDigit = Integer.parseInt(Integer.toString(copyBinary).substring(5, 6));
int seventhDigit = Integer.parseInt(Integer.toString(copyBinary).substring(6, 7));
int eigthDigit = Integer.parseInt(Integer.toString(copyBinary).substring(7));
firstDigit = firstDigit*128;
secondDigit = secondDigit*64;
thirdDigit = thirdDigit*32;
fourthDigit = fourthDigit*16;
fifthDigit = fifthDigit*8;
sixthDigit = sixthDigit*4;
seventhDigit = seventhDigit*2;
eigthDigit = eigthDigit*1;
System.out.println(firstDigit+" "+secondDigit+" " +thirdDigit+" "+fourthDigit+" "+fifthDigit+" "+sixthDigit+" "+seventhDigit+" "+eigthDigit);
System.out.println(copyBinary + " in decimal form is " + (firstDigit+secondDigit+thirdDigit+fourthDigit+fifthDigit+sixthDigit+seventhDigit+eigthDigit));
}
}

Leading zeros are ignored when you parse and format an int. The simplest solution is to keep the full value as a string and only then parse the individual digits:
String binary = keyboard.next();
int firstDigit = Integer.parseInt(binary.substring(0, 1));
// etc.

What I proposed in the comments is to read the whole input as string and then convert one character at the time to integer
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter an 8-bit binary number:");
String input = keyboard.nextLine();
// need to validate input here
int dec = 0;
for (int i=0; i<input.length(); i++) {
int x = Character.getNumericValue(input.charAt(input.length()-1-i));
dec += x * Math.pow(2, i);
}
System.out.println("For binary number " + input + " its decimal value is " + dec);

How to read each individual digit of a number in Java

I am trying to run a program that outputs the sum of every digit of an entered in integer. How would I go about reading the number and outputting each digit?
Example: Input is 4053 the output would be "4+0+5+3 = 12".
import java.util.Scanner;
public class Digits{
public static void main(String args[]) {
//Scans in integer
Scanner stdin = new Scanner(System.in);
System.out.println("Enter in a number: ");
int number = stdin.nextInt();
//Set sum to zero for reference
int sum = 0;
int num = number; //Set num equal to number as reference
//reads each digit of the scanned number and individually adds them together
//as it goes through the digits, keep dividing by 10 until its 0.
while (num > 0) {
int lastDigit = num % 10;
sum = sum + lastDigit;
num = num/10;
}
}
}
That is the code I used for calculating the sum of the individual digits, now I just need help with outputting the individual digits. Any tips and tricks would be much appreciated.

import java.util.Scanner;
public class Digits{
public static void main(String args[]) {
//Scans in integer
Scanner stdin = new Scanner(System.in);
System.out.println("Enter in a number: ");
int number = stdin.nextInt();
//Set sum to zero for reference
int sum = 0;
int num = number; //Set num equal to number as reference
//reads each digit of the scanned number and individually adds them together
//as it goes through the digits, keep dividing by 10 until its 0.
String numToString = "";
while (num > 0) {
int lastDigit = num % 10;
numToString +=lastDigit+" + ";
sum = sum + lastDigit;
num = num/10;
}
//eliminate the last + sign
numToString = numToString.substring(0,numToString.lastIndexOf("+")).trim();
System.out.println(numToString +" = " +sum);
}
}

I am not sure what you mean by outputting but instead of this you can read the number as string and take each character and parse it to integers
Scanner stdin = new Scanner(System.in);
System.out.println("Enter in a number: ");
String number = stdin.next();
int[] result = new int[number.length];
for(int i=0;i<number.length;i++) {
result[i] = Integer.parseInt(number.charAt(i)+"");
}
return result;

You may read this like String and then divided by the number.
final Scanner s = new Scanner ( System.in );
final String line = s.nextLine ().trim ();
final char [] array = line.toCharArray ();
int sum = 0;
for ( final char c : array )
{
if ( !Character.isDigit ( c ) )
{
throw new IllegalArgumentException ();
}
sum = sum + Character.getNumericValue ( c );
}
System.out.println ( "sum = " + sum );

without a scanner you can do
StringBuilder sb = new StringBuilder();
String sep = "";
int ch;
long sum = 0;
while((ch = System.in.read()) > ' ') {
if (ch < '0' || ch > '9') {
System.out.println("Skipping " + (char) ch);
continue;
}
sb.append(sep).append((char) ch);
sep = " + ";
sum += ch - '0';
}
sb.append(" = ").append(sum);
System.out.println(sb);

Try this:
import java.util.*;
public class Digits {
public static void main(String [] args)
{
Scanner input = new Scanner (System.in);
System.out.println("Enter number -> ");
int number = input.nextInt();
int sum = 0;
String numStr = "" + number;
while(number > 0)
{
int lastDigit = number % 10;
sum += lastDigit;
number = number / 10;
}
for(int i = 0; i < numStr.length();i++)
{
System.out.print(numStr.charAt(i));
// Dont print an extra + operator at the end
if( i == numStr.length() - 1) continue;
else
System.out.print(" + ");
}
System.out.print(" = " + sum);
}
}

Having trouble converting a character value to an integer value

import java.util.Scanner;
public class baseConverter {
//Main method
public static void main(String[] args){
Scanner keyboard = new Scanner(System.in);
String input = "";
System.out.println("What number base would you like to convert?");
int base = keyboard.nextInt();
//Checking if the base is between 2 and 9, inclusive
if (base >= 2 && base <=9){
System.out.println("Please enter a base " + base + " number:");
}else{
System.out.println("Please enter a base from 2 to 9");
}
input = keyboard.next();
int converted = compute(input, base);
System.out.println("The base-10 conversion of that number is " + converted);
}
//Where all the conversion will take place
public static int compute(String userString, int userBase){
int n = userString.length(), output = 0;
int[] num = new int[n];
//The for loop that does all the computing
for (int i = 1; i <= n; i++){
//assigning values to the array indeces
num[i-1] = Integer.parseInt(String.valueOf(userString.charAt(i-1)));
if(num[i-1] != 0){
output = output + ((userBase ^ (n-i)) * (num[i-1]-1));
}else{
output = output;
}
}
System.out.println("User base is " + userBase+ ". n is "+ n);
return output;
}
}
When I run this and input the base and 3 and the input as 2, it seems to convert the value '2' to it's ASCII value of 50 when storing it in the num array. I guess my question is if there is any way that I could work around this or what an entirely different way of getting the value from the string stored as an integer.

Random Data Generator integers and Characters

I have to Create a RandomDataGenerator. The code I have kind of works, but I am having trouble with some parts of it. The fist issue I am having is with the integers. this is what I get when I run it:
run:
What do you want to generate?
i = integer, d = double, c = char
i
How many integers do you want?
10
Choose low value for your integer:
3
Choose high value for your integer:
7
Integers:
4
3
6
6
6
5
2
3
5
6
It gives me the 10 numbers, but it is not supposed to go lower than 3.
The other issue I'm having is with the characters this is what I get
run:
What do you want to generate?
i = integer, d = double, c = char
c
How many characters do you want?
5
Choose low limit for your character:
C
Choose high limit for your character:
S
P
false
how can I fix this problems?
package javaapplication5;
import java.util.Random;
import java.util.Scanner;
public class JavaApplication5 {
private static int a;
public static void main(String[] args) {
System.out.println("What do you want to generate? ");
System.out.println("i = integer, d = double, c = char" );
char i, d, c;
int low_int = 0,high_int = 0, quant_int = 0;
double low_double = 0, high_double = 0, quant_double = 0;
char low_char = 0, high_char = 0, quant_char = 0;
int result = 0;
String input;
Scanner in = new Scanner (System.in);
String A= in.next();
int largo = A.length();
char select []= new char [largo];
select[a]=A.charAt(a);
for(int q=0; q<largo;q++){
if (select[q]=='i') {
System.out.println( " How many integers do you want? ");
Scanner Integerswanted = new Scanner(System.in);
String B= in.next();
quant_int = Integer.parseInt(B);
System.out.println( " Choose low value for your integer: ");
Scanner LoVa = new Scanner(System.in);
String LV= in.next();
low_int = Integer.parseInt(LV);
System.out.println( " Choose high value for your integer: ");
Scanner HiVa = new Scanner(System.in);
String hV= in.next();
high_int = Integer.parseInt(hV);
System.out.println( " Integers: ");
int random_generator = JavaApplication5.random_generator(quant_int, low_int, high_int);
int s = random_generator;
if(s>low_int && s<high_int){
}
}
else if (select[q]=='d'){
System.out.println( " How many doubles do you want? ");
Scanner DoublesWanted = new Scanner(System.in);
String R= in.next();
quant_double = Double.parseDouble(R);
System.out.println(" Choose low value for your double: ");
Scanner LoDo = new Scanner(System.in);
String LD= in.next();
low_double = Double.parseDouble(LD);
System.out.println(" Choose high value for your double: ");
Scanner HiDo = new Scanner(System.in);
String HD= in.next();
high_double = Double.parseDouble(HD);
System.out.println( " Doubles: ");
double random_generator = JavaApplication5.random_generator(quant_double, low_double, high_double);
double k = random_generator;
}
else if (select[q]=='c'){
System.out.println( " How many characters do you want? ");
Scanner CharWanted = new Scanner(System.in);
String Cw= in.next();
quant_char = A.charAt(0);
System.out.println( " Choose low limit for your character: ");
Scanner LoCh = new Scanner(System.in);
String LC= in.next();
low_char = A.charAt(0);
System.out.println( " Choose high limit for your character: ");
Scanner HiCh = new Scanner(System.in);
String HC= in.next();
high_char = A.charAt(0);
char random_generator = JavaApplication5.random_generator(quant_char, low_char, high_char);
char e = random_generator;
} }}
public static int random_generator(int quant, int low, int high){
Random rand_num = new Random();
int return_int = 0;
for(int z = low; z <= quant + 2 ; z++)
System.out.println(rand_num.nextInt(high) + 1 );
return return_int;
}
public static double random_generator(double quant, double low, double high){
Random rand_num = new Random();
double return_double = 0;
for(double z = low; z <quant + 2; z++) {
System.out.println(rand_num.nextDouble() + low );
}
return return_double;
}
public static char random_generator(char quant, char low, char high){
String [] abecedario = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J",
"K", "L", "M","N","O","P","Q","R","S","T","U","V","W", "X","Y","Z" };
int Rand_num = (int) Math.round(Math.random() * 26 ) ;
System.out.println( abecedario[Rand_num] );Random
rand_num = new Random();
char return_char = 0;
for(double z = low; z < quant + 1; z++)
System.out.println(abecedario[Rand_num].equals(high));
return return_char;
}
}

For the integer, you should use:
rand_num.nextInt(high - low) + high;
For the Character, you should use the same thing except you need to typecast it to a character after you find the random integer.
(char)rand_num.nextInt(high - low) + high;

How to convert octal to decimal in the different form without using APIs?

I tried to convert octal to decimal and I got some output but I am not satisfied with it. Can anyone give an idea how to convert a different model without using API-s?
public static void main(String args[]){
System.out.print("Enter the number to convert");
Scanner ss =new Scanner(System.in);
int a = ss.nextInt();
int b = ss.nextInt();
int c = ss.nextInt();
int d = ss.nextInt();
int temp =(a*(8*8*8));
int temp1 =(b*(8*8));
int temp2 =(c*(8));
int temp3 =(d*(1));
System.out.println("The decimal is " +"\n" + (temp +temp1 +temp2 +temp3))
}

Try this one:
public static void main(String[] args)throws IOException
{
BufferedReader reader =
new BufferedReader(new InputStreamReader(System.in));
String oct = reader.readLine();
int i= Integer.parseInt(oct,8);
System.out.println("Decimal:=" + i);
}

I havn't try this but try to get a logic,
take input in a string then
String s ; //for input
String answer ="";
for(a=0,b=s.length-1;b>=0;b--)
{
int digit =Integer.parseInt(s.charAt(a));
int ans = (int)(digit * Math.pow(8,b));
answer+=ans;
a++;
}

Maybe my version is something you are looking for:
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
System.out.println("Please enter a number: ");
String numberString = sc.nextLine();
int[] eachNumbers = new int[numberString.length()];
for(int i = 0; i < eachNumbers.length; i++){
eachNumbers[i] = Integer.parseInt(numberString.substring(i, i+1));
}
int digit = 0;
for(int i = 0; i < eachNumbers.length; i++){
if(eachNumbers.length > 1){
digit += (eachNumbers[i] * Math.pow(8, eachNumbers.length - (i+1)));
}else{
digit += (eachNumbers[i] * 1);
}
}
System.out.println("The Octal " + numberString + " as Decimal is " + digit);
}
I know there is alot that can be made better but I'm still learning and wanted to help you :)