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How to Get Rid of These Extra Spaces?

This program asks to list out all the possible years which are leap years from 2014 to 2114, which I did correctly in the program shown below and the years to be listed with a space in each with 10 in every row. Once 10 years are listed, you go to the next. line. The only problem which I notice is that there are 3 empty lines between every 10 rows of years. How can I alter the program so there are no spaces between these rows.
public class fiveTwoSeven {
public static void main(String[] args)
{
int year2 = 2114;
int count = 0;
for (int year1 = 2014; year1 <= year2; year1++)
{
if (year1 % 4 == 0 && !(year1 % 100 == 0))
{
System.out.print(year1 + " ");
count++;
}
if (count % 10 == 0 && !(count == 0))
{
System.out.println();
}
}
}
}

Just change your second if condition block to this:
if (count % 10 == 0 && !(count == 0))
{
System.out.println();
count = 0;
}
It is creating problem when count is 10 or 20 or 30 or ....
I am giving explanation for 10...
From 2014, according to your logic 10th leap year is 2052. So after printing 2052, you are printing a new line. And for 2053, 2054 and 2055, your count is still 10. So second if block is printing another new line for each one.

Try it:
if (count % 10 == 0 && !(count == 0))
{
System.out.println();
count = 0;
}
Or
int year2 = 2114;
int count = 0;
for (int year1 = 2014; year1 <= year2; year1++)
{
if (year1 % 4 == 0 && !(year1 % 100 == 0))
{
count++;
System.out.print(year1 + " ");
if(count % 10 == 0 && !(count == 0)) {
System.out.println();
count = 0;
}
}
}
Output:
Note:
You just need to reset the value of count after it reaches to 10 so that cursor goes to the next line.

You should only println() in your if block (since that is when you output leap years). More importantly, your algorithm has a bug. Years that are multiples of 400 are leap years (2000 and 2400 are both leap years). I suggest you save the leap year as a local boolean. Something like,
public static void main(String[] args) {
int count = 0, year1 = 2014, year2 = 2114;
for (; year1 <= year2; year1++) {
boolean leapYear = false;
if (year1 % 4 == 0) {
if (year1 % 100 != 0) {
leapYear = true;
} else if (year1 % 400 == 0) {
leapYear = true;
}
}
if (leapYear) {
System.out.print(year1 + " ");
count++;
if (count % 10 == 0) {
System.out.println();
}
}
}
}

I keep getting the wrong numbers from my program

I am trying to write a program where the user inputs 2 dates and the program calculates the days in between (without using any of the calendar classes) and prints the results, but I keep getting crazy numbers that make no sense. When I tried to make it calculate 5 days it printed the results of 333 and when I try to do something like 20 years it prints numbers in the millions.
import java.util.Scanner;
public class DaysCalc {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("Please enter starting date (mm-dd-yyyy) ");
String startingdate = input.next();
System.out.print("Please enter ending date (mm-dd-yyyy) ");
String finishingdate = input.next();
String startingdayst = startingdate.substring(3, 5);
String startingmonthst = startingdate.substring(0, 2);
String startingyearst = startingdate.substring(6, 10);
String finishingdayst = finishingdate.substring(3, 5);
String finishingmonthst = finishingdate.substring(0, 2);
String finishingyearst = finishingdate.substring(6, 10);
int startingyear = Integer.parseInt(startingyearst);
int startingday = Integer.parseInt(startingdayst);
int startingmonth = Integer.parseInt(startingmonthst);
int finishingyear = Integer.parseInt(finishingyearst);
int finishingday = Integer.parseInt(finishingdayst);
int finishingmonth = Integer.parseInt(finishingmonthst);
System.out.println(startingyear + "," + startingday + "," + startingmonth );
System.out.println(finishingyear + "," + finishingday + "," + finishingmonth);
int daysLeft = 0;
int daysUntilEnd = 0;
int i = 0;
daysLeft = daysInAMonth(startingmonth, startingyear) - startingday;
daysUntilEnd = finishingday;
for (int monthCount = startingmonth + 1; monthCount <= 12; monthCount++)
{
i += daysInAMonth(monthCount, startingyear);
}
for (int yearCount = startingyear + 1; yearCount <= finishingyear; yearCount++)
{
if (isLeapYear(yearCount))
{
i = i * 366;
}
else
{
i = i * 365;
}
i += daysUntilEnd;
}
System.out.println(i);
}
private static boolean isLeapYear(int year) {
boolean isLeapYear = ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0));
return isLeapYear;
}
private static int daysInAMonth(int month, int year) {
if (month == 2)
{
if (isLeapYear(year) )
{
return 29;
}
else
{
return 28;
}
}
if (month == 1 || month == 3 || month == 5 || month == 7 || month == 9 || month == 11) {
return 31;
}
return 30;
}
}

the problem was with this part
for (int monthCount = startingmonth + 1; monthCount < finishingmonth; monthCount++)
{
i += daysInAMonth(monthCount, startingyear);
}
for (int yearCount = startingyear + 1; yearCount <= finishingyear; yearCount++)
{
if (isLeapYear(yearCount))
{
i = i + 366;
}
else
{
i = i + 365;
}
}
i += daysUntilEnd;
i += daysInAMonth(startingmonth, startingyear)-startingday-1;
System.out.println(i);
it's not completely bug free but i hope it helps you to see where it went wrong. it was kind of an eye mistake

java - how to efficiently categorize user input

I'm trying to make a simple program that reads the user inputted integer and categorizes it based on the value until the counter reaches 70.
Code:
int counter = 0;
int value;
int a = 0;
int b = 0;
int c = 0;
int d = 0;
int e = 0;
int i = 0;
Scanner scan = new Scanner(System.in);
while (counter != 70) {
value = scan.nextInt();
if (value >= 45 && value <= 55) {
a++;
counter++;
} else if (value >= 56 && value <= 66) {
b++;
counter++;
} else if (value >= 67 && value <= 77) {
c++;
counter++;
} else if (value >= 78 && value <= 88) {
d++;
counter++;
} else if (value >= 89 && value <= 99) {
e++;
counter++;
} else if (value >= 100 && value <= 110) {
i++;
counter++;
} else {
}
}
System.out.println(a + "-" + b + "-" + c + "-" + d + "-" + e + "-" + i);
Obviously, this code is inefficient and I know for a fact that there are less time consuming ways to replicate this. I feel pretty dumb right now so please tell me the most efficient way.

Also if doing a certain number of time, the I feel a for loop is clearer.
consider using an array of ints rather than a-i
int [] values = new int [6];
Scanner scan = new Scanner(System.in);
for (int counter = 0; counter < 70; counter++)
{
int value = scan.nextInt();
if (value >= 45 && value <= 55) {
values[0]++;
} else if (value >= 56 && value <= 66) {
values[1]++;
} else if (value >= 67 && value <= 77) {
values[2]++;
} else if (value >= 78 && value <= 88) {
values[3]++;
} else if (value >= 89 && value <= 99) {
values[4]++;
} else if (value >= 100 && value <= 110) {
values[5]++;
} else {
counter--; // out of bounds - try again
}
}

Try this.
int counter = 0;
int[] a = new int[6];
Scanner scan = new Scanner(System.in);
while (counter < 70) {
int value = scan.nextInt();
if (value >= 45 && value <= 110) {
a[(value - 45) / 11]++;
counter++;
}
}
System.out.print(a[0]);
for (int i = 1; i < a.length; ++i)
System.out.print("-" + a[i]);
System.out.println();

I've been thinking how to make this program with loops so this is what I came up with:
int min = 45;
int max = 55;
int counter = 0;
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 10; i++) {
list.add(scan.nextInt());
}
while (min <= 100) {
for (int value : list) {
if (value >= min && value <= max) {
counter++;
}
}
System.out.print(counter + "-");
min += 11;
max += 11;
counter = 0;
I really have no idea if this allocates memory faster or not but to me, it looks tidier although it may not be efficient.

One way to improve readability is to change variables names:
a becomes from45to55
b becomes from56to66
You can also move repeated operations into one method:
public static void increment(int value, int counter) {
value++;
counter++;
}
And use try with resources block to close Scanner. Full code:
public static void main(String[] args) {
int counter = 0;
int value;
int from45to55 = 0;
int from56to66 = 0;
int from67to77 = 0;
int from78to88 = 0;
int from89to99 = 0;
int from100to110 = 0;
try (Scanner scan = new Scanner(System.in)) {
while (counter != 70) {
value = scan.nextInt();
if (value >= 45 && value <= 55) {
increment(from45to55, counter);
} else if (value >= 56 && value <= 66) {
increment(from56to66, counter);
} else if (value >= 67 && value <= 77) {
increment(from67to77, counter);
} else if (value >= 78 && value <= 88) {
increment(from78to88, counter);
} else if (value >= 89 && value <= 99) {
increment(from89to99, counter);
} else if (value >= 100 && value <= 110) {
increment(from100to110, counter);
} else {
}
}
}
}
public static void increment(int value, int counter) {
value++;
counter++;
}

Can't figure out the error Luhn check

Its supose to tell me if a card is valid or invalid using luhn check
4388576018402626 invalid
4388576018410707 valid
but it keeps telling me that everything is invalid :/
Any tips on what to do, or where to look, would be amazing. I have been stuck for a few hours.
It would also help if people tell me any tips on how to find why a code is not working as intended.
im using eclipse and java
public class Task11 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a credit card number as a long integer: ");
long number = input.nextLong();
if (isValid(number)) {
System.out.println(number + " is valid");
} else {
System.out.println(number + " is invalid");
}
}
public static boolean isValid(long number) {
return (getSize(number) >= 13) && (getSize(number) <= 16)
&& (prefixMatched(number, 4) || prefixMatched(number, 5) || prefixMatched(number, 6) || prefixMatched(number, 37))
&& (sumOfDoubleEvenPlace(number) + sumOfOddPlace(number)) % 10 == 0;
}
public static int sumOfDoubleEvenPlace(long number) {
int result = 0;
long start = 0;
String digits = Long.toString(number);
if ((digits.length() % 2) == 0) {
start = digits.length() - 1;
} else {
start = digits.length() - 2;
}
while (start != 0) {
result += (int) ((((start % 10) * 2) % 10) + (((start % 10) * 2) / 2));
start = start / 100;
}
return result;
}
public static int getDigit(int number) {
return number % 10 + (number / 10);
}
public static int sumOfOddPlace(long number) {
int result = 0;
while (number != 0) {
result += (int) (number % 10);
number = number / 100;
}
return result;
}
public static boolean prefixMatched(long number, int d) {
return getPrefix(number, getSize(d)) == d;
}
public static int getSize(long d) {
int numberOfDigits = 0;
String sizeString = Long.toString(d);
numberOfDigits = sizeString.length();
return numberOfDigits;
}
public static long getPrefix(long number, int k) {
String size = Long.toString(number);
if (size.length() <= k) {
return number;
} else {
return Long.parseLong(size.substring(0, k));
}
}
}

You should modiffy your isValid() method to write down when it doesn't work, like this:
public static boolean isValid(long number) {
System.err.println();
if(getSize(number) < 13){
System.out.println("Err: Number "+number+" is too short");
return false;
} else if (getSize(number) > 16){
public static boolean isValid(long number) {
System.err.println();
if(getSize(number) < 13){
System.out.println("Err: Number "+number+" is too short");
return false;
} else if (getSize(number) > 16){
System.out.println("Err: Number "+number+" is too long");
return false;
} else if (! (prefixMatched(number, 4) || prefixMatched(number, 5) || prefixMatched(number, 6) || prefixMatched(number, 37)) ){
System.out.println("Err: Number "+number+" prefix doesn't match");
return false;
} else if( (sumOfDoubleEvenPlace(number) + sumOfOddPlace(number)) % 10 != 0){
System.out.println("Err: Number "+number+" doesn't have sum of odd and evens % 10. ");
return false;
}
return true;
}
My guess for your problem is on the getPrefix() method, you should add some logs here too.
EDIT: so, got more time to help you (don't know if it's still necessary but anyway). Also, I corrected the method I wrote, there were some errors (like, the opposite of getSize(number) >= 13 is getSize(number) < 13)...
First it will be faster to test with a set of data instead of entering the values each time yourself (add the values you want to check):
public static void main(String[] args) {
long[] luhnCheckSet = {
0, // too short
1111111111111111111L, // too long (19)
222222222222222l // prefix doesn't match
4388576018402626l, // should work ?
};
//System.out.print("Enter a credit card number as a long integer: ");
//long number = input.nextLong();
for(long number : luhnCheckSet){
System.out.println("Checking number: "+number);
if (isValid(number)) {
System.out.println(number + " is valid");
} else {
System.out.println(number + " is invalid");
}
System.out.println("-");
}
}
I don't know the details of this, but I think you should work with String all along, and parse to long only if needed (if number is more than 19 characters, it might not parse it long).
Still, going with longs.
I detailed your getPrefix() with more logs AND put the d in parameter in long (it's good habit to be carefull what primitive types you compare):
public static boolean prefixMatched(long number, long d) {
int prefixSize = getSize(d);
long numberPrefix = getPrefix(number, prefixSize);
System.out.println("Testing prefix of size "+prefixSize+" from number: "+number+". Prefix is: "+numberPrefix+", should be:"+d+", are they equals ? "+(numberPrefix == d));
return numberPrefix == d;
}
Still don't know what's wrong with this code, but it looks like it comes from the last test:
I didn't do it but you should make one method from sumOfDoubleEvenPlace(number) + sumOfOddPlace(number)) % 10 and log both numbers and the sum (like i did in prefixMatched() ). Add logs in both method to be sure it gets the result you want/ works like it should.
Have you used a debugger ? if you can, do it, it can be faster than adding a lot of logs !
Good luck

EDIT:
Here are the working functions and below I provided a shorter, more efficient solution too:
public class CreditCardValidation {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int count = 0;
long array[] = new long [16];
do
{
count = 0;
array = new long [16];
System.out.print("Enter your Credit Card Number : ");
long number = in.nextLong();
for (int i = 0; number != 0; i++) {
array[i] = number % 10;
number = number / 10;
count++;
}
}
while(count < 13);
if ((array[count - 1] == 4) || (array[count - 1] == 5) || (array[count- 1] == 3 && array[count - 2] == 7)){
if (isValid(array) == true) {
System.out.println("\n The Credit Card Number is Valid. ");
} else {
System.out.println("\n The Credit Card Number is Invalid. ");
}
} else{
System.out.println("\n The Credit Card Number is Invalid. ");
}
in.close();
}
public static boolean isValid(long[] array) {
int total = sumOfDoubleEvenPlace(array) + sumOfOddPlace(array);
if ((total % 10 == 0)) {
for (int i=0; i< array.length; i++){
System.out.println(array[i]);}
return true;
} else {
for (int i=0; i< array.length; i++){
System.out.println(array[i]);}
return false;
}
}
public static int getDigit(int number) {
if (number <= 9) {
return number;
} else {
int firstDigit = number % 10;
int secondDigit = (int) (number / 10);
return firstDigit + secondDigit;
}
}
public static int sumOfOddPlace(long[] array) {
int result = 0;
for (int i=0; i< array.length; i++)
{
while (array[i] > 0) {
result += (int) (array[i] % 10);
array[i] = array[i] / 100;
}
}
System.out.println("\n The sum of odd place is " + result);
return result;
}
public static int sumOfDoubleEvenPlace(long[] array) {
int result = 0;
long temp = 0;
for (int i=0; i< array.length; i++){
while (array[i] > 0) {
temp = array[i] % 100;
result += getDigit((int) (temp / 10) * 2);
array[i] = array[i] / 100;
}
}
System.out.println("\n The sum of double even place is " + result);
return result;
}
}
I also found a solution with less lines of logic. I know you're probably searching for an OO approach with functions, building from this could be of some help.
Similar question regarding error in Luhn algorithm logic:
Check Credit Card Validity using Luhn Algorithm
Link to shorter solution:
https://code.google.com/p/gnuc-credit-card-checker/source/browse/trunk/CCCheckerPro/src/com/gnuc/java/ccc/Luhn.java
And here I tested the solution with real CC numbers:
public class CreditCardValidation{
public static boolean Check(String ccNumber)
{
int sum = 0;
boolean alternate = false;
for (int i = ccNumber.length() - 1; i >= 0; i--)
{
int n = Integer.parseInt(ccNumber.substring(i, i + 1));
if (alternate)
{
n *= 2;
if (n > 9)
{
n = (n % 10) + 1;
}
}
sum += n;
alternate = !alternate;
}
return (sum % 10 == 0);
}
public static void main(String[] args){
//String num = "REPLACE WITH VALID NUMBER"; //Valid
String num = REPLACE WITH INVALID NUMBER; //Invalid
num = num.trim();
if(Check(num)){
System.out.println("Valid");
}
else
System.out.println("Invalid");
//Check();
}
}

How can I get this program to print out ten items per line seperated by 1 space?

Here's my code so far
public class DivisibleBy5and6
{
public static void main (String []args)
{
for (int i = 100; i <= 200; i++)
{
boolean num = (i % 5 == 0 || i % 6 == 0) && !(i % 5 == 0 && i % 6 == 0);
if (num == true)
System.out.println(i + " is divisible");
}
}
}
Like stated previously how can I get the output to print out 10 items per line separated by a space?

How about:
int count = 0;
for (int i = 100; i <= 200; i++) {
boolean num = (i % 5 == 0 || i % 6 == 0) && !(i % 5 == 0 && i % 6 == 0);
if (num == true) {
count++;
System.out.print(i + " is divisible ");
if(count >= 10) {
System.out.println();
count -= 10;
}
}
}