Develop Reference

how do I display the correct output when no positve numbers are entered

I'm new to coding. Assignment is to calculate the average of all the positive numbers input and exit when a zero is input. If no positive numbers are input display a message average not possible.
The following is what I have so far. I am stuck on the part about printing out the message "cannot calculate the average" when only a zero or negative numbers are input.
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int numbers = 0;
int sumOfNumbers = 0;
double averagePositive = 0;
while (true) {
System.out.println("Give a number: ");
int number = Integer.valueOf(scanner.nextLine());
if (number == 0)
break;
if (number > 0)
sumOfNumbers = number + sumOfNumbers;
if (number > 0)
numbers = numbers + 1;
if (number > 0)
averagePositive = (double)sumOfNumbers / (double)numbers;
}
System.out.println(averagePositive);
}

Try it as follows...
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Give a number: ");
int num=input.nextInt();
int tot=0; //total
int count=0; // counting the positive numbers
if(num>0){
while(num!=0){
tot+=num;
count++;
System.out.print("Give a number: ");
num=input.nextInt();
if(num<0){
System.out.print("Not possible");
return;
}
}
double avg =(double)tot/n;
System.out.print("Average: "+avg);
}else{
System.out.println("Cannot calculate the average.");
}
}

I'd probably do it like this to keep it simple. Also in general, try not to cramp code together. Most formal project demand a certain degree of styling and usually spaces between operators and braces, etc... is required. In the long run it makes the code more readable and easier to maintain.
In your code there was no need to repeat the same if test for number > 0 multiple times, they could have all been bundled together. If the program was bigger and more complex I may have named the variable names with more qualification but for a short program like this, brief names were sufficient for clarity.
continue and break are important keywords to control loop behavior and can be used to increase brevity and clarity. continue goes back to the top of the loop immediately and break exits the innermost loop immediately. Dividing a double by an int yields a double so I was able to eliminate a cast. And the += operator makes it a little easier to read the line.
Also in Java and C any if() or else clause that contains one line doesn't require braces and unless a program is nested in such a way that adding the braces anyway adds to the clarity, it is often clearer to omit the braces in that case. The if statement illustrates both ways in a single statement.
import java.util.Scanner;
public class avg
{
static int count = 0;
static double sum = 0;
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("\nEnter a sequence of positive numbers (0 to calculate average):\n");
while (true) {
System.out.print("Number? ");
int n = scanner.nextInt();
if (n < 0) {
System.out.println("Negative numbers not allowed.");
continue;
} else if (n == 0)
break;
sum += (double)n;
++count;
}
System.out.println("Average of " + count + " numbers = " +
(double)(sum / count) + "\n");
System.exit(1);
}
}
Sample output:
$ java avg
Enter a sequence of positive numbers (0 to calculate average)
Number? 1
Number? 2
Number? 3
Number? 4
Number? 5
Number? -6
Negative numbers not allowed.
Number? 0
Average of 5 numbers = 3.0

How can I display the numbers in a for loop from 1-entered value?

So I am working on this homework problem called "pennies for pay" and I am basically done except for one issue. My for loop prints out the number of the inputted number that many times if that makes sense?
public class Assignment3 {
public static void main(String[] args) {
//INITIAL VARIABLES
int workdays;
double money;
double total = 0;
double add;
//GATHERING NUMBER OF DAYS WORKED
System.out.println("For how many days will the pay double? ");
Scanner a = new Scanner(System.in);
workdays = a.nextInt();
//PARTIAL OUTPUT
System.out.println("Day\t\tTotal Pay");
System.out.println("__________________________");
//FOR LOOP
for(int payday = 1; payday <= workdays;payday++){
money = Math.pow(2,payday - 1);
System.out.println(workdays +"\t$\t"+ money/100);
total = total + money/100;
}
//MORE OUTPUT
System.out.println("__________________________");
System.out.println("Total\t$\t" + total );
}
}
When I input 12 for days, the number 12 repeats itself 12 times. how can I get it to go from 1-12 please and thank you.

In your for loop you are printing the variable workdays in which it's value doesn't change inside the loop, that means it's constant.Since your target is to output pennies per day you should try this code if it helps
for(int payday = 1; payday <= workdays; payday++){
money = Math.pow(2,payday - 1);
System.out.println(payday + "\t$\t" + money/100);
total += money/100;
}

The value of workdays variable is always 12 if you input 12. In your System.out.println inside the loop, use payday instead of workdays. Because payday is the one being incremented for each iteration.
That should fix it.

D&D Character stat roller (Java)

So I am very new to the Java language and I'm attempting to put together a dice roller of sorts for character stat generation for D&D (Dungeons and Dragons).
What I want the program to do is roll x number of D6, x amount of times. X is to be input by the user. I also need the program to ask if it is to re-roll a result of 1 on a D6 roll. Plus, the program must only keep the highest 3 numbers of the rolled dice. It then needs to output the results of each grouping of dice rolls, instead of totaling them all together.
So an example would be: I want 4 D6 rolled 6 times, and re-roll 1's.
The program output would be something along the lines of:
Your results are:
10
12
13
15
17
11.
I'm trying to write this with 3 classes, though I know it doesn't need to have 3 classes to operate. The additional classes are more of a requirement from a project standpoint.
I've managed to code what is necessary to roll a single dice, but as I said I'm very new and have almost zero idea on where to go with this.
The code I have so far is:
//Scanner is implemented in preparation for user input as more coding is
//added
import java.util.Scanner;
public class RollDie {
public static void main(String[] args) {
int SIDES = 6; // how many sides on the die?
// roll should be 1 through SIDES
int roll = (int) (Math.random() * SIDES) + 1;
// print result
System.out.println(roll);
}
}

A one-class solution with freindly user input could look like this:
private final static int SIDES = 6;
public static void main(String[] args) {
java.util.Scanner scanner = new java.util.Scanner (System.in);
System.out.println("Number of dice?");
final int dice = scanner.nextInt();
System.out.println("Number of rolls?");
final int rolls = scanner.nextInt();
System.out.println("Reroll result 1? Enter y for yes");
final boolean reroll = scanner.next().equals("y");
for (int r = 0; r < rolls; r++) {
int allDice = 0;
for (int d = 0; d < dice; d++) {
int roll = (int) (Math.random() * SIDES) + 1;
while (reroll && roll == 1) {
roll = (int) (Math.random() * SIDES) + 1;
}
allDice += roll;
}
System.out.println(allDice);
}
}

How do i recognize 2 digits as separated digits?

So basically the assignment says i need to get a number 'n' from the user and for all the numbers between 1 to 'n' code the program to print all the numbers divided by 3 without residue && print ONLY the numbers that both (or one) of their digits equal to 5 or less, for example if the user give 22 the programs prints 3,12,21.
thats what ive done by now (the place i putted a question mark is where im having hard time to figure out what to do) so this code in not compiled yet :
public static void main(String[] args) {
Scanner get = new Scanner(System.in);
int num;
System.out.println("Enter A Random Number: ");
num = get.nextInt();
for (int i=1;i>0 && i<=num;i++) {
if (i%3==0 && ?)
System.out.println(i);

I'm a bit confused about the second part of your question but based on the first part and what I got from the second part ( that the sum of the digits of numbers that is equal or less to 5 should only be printed )
Here is the code for your program : (It should work perfectly, update me if you find any problems)
public static void main(String[] args) {
Scanner get = new Scanner(System.in);
int num;
System.out.println("User please enter a number of your choice : ");
num = get.nextInt();
for(int x = 1 ; x < num ; x++){
String number = ""+ x ;
int sum = 0 ;
for(int i = 0 ; i < number.length() ; i ++ ){
sum +=number.charAt(i)-'0' ; }
if(x % 3 == 0 && sum <= 5){
System.out.println(x) ; }
sum = 0 ;
}
}

divided by 3 without residue
If you understand what "without residue" means, then I assume you are familiar with modulo arithmetic. In programming, we have the modulo operator % which returns the remainder from a division. So 25 % 8 evaluates to 1. You can use this to get the digits of a number 21 % 10 evalutes to 1 which is exactly the ones digit. To get the the tens digit, we need to divide by 10 first 21 / 10 % 10 evaluates to 2. This works because integer division throws away the remainder.

This will do. So, you have to go through every digit so, I converted it into a string and then matched the regex for 1 to 5 on that character and then put it back in another string and it solves it.
public static void main(String[] args) {
Scanner get = new Scanner(System.in);
int num;
System.out.println("Enter A Random Number: ");
num =Integer.parseInt(get.nextLine());
for(int i =1;i<=num; i++){
if(i%3==0){
String input = Integer.toString(i);
String toPrint = "";
for(int j =0 ; j<input.length();j++){
if(Character.toString(input.charAt(j)).matches("^[1-5]$")){
toPrint+=Character.toString(input.charAt(j));
}
}
//check the length to avoid cases like 30,60 etc.
if(input.length()==toPrint.length()){
System.out.println(toPrint);
}
}
}
}

for loop structure

This program will calculate the average grade for 4 exams using a for loop by prompting
the user for exam grades, one at a time, then calculate the average and display the result.
public class ExamsFor4 {
public static void main(String[] arguments) {
int inputNumber; // One of the exams input by the user.
int sum = 0; // The sum of the exams.
int i; // Number of exams.
Double Avg; // The average of the exams.
TextIO.put("Please enter the first exam: "); // get the first exam.
inputNumber = TextIO.getlnInt();
for ( i = 1; i <= 4; i++ ) {
sum += inputNumber; // Add inputNumber to running sum.
TextIO.put("Please enter the next exam: "); // get the next exam.
inputNumber = TextIO.getlnInt();
if (i == 4) {
Avg = ((double)sum) / i;
TextIO.putln();
TextIO.putln("The total sum for all " + i +" exams is " + sum);
TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);
break;
}
}
} // end main ()
} // end class ExamsFor4
My result:
Please enter the first exam: 100
Please enter the next exam: 99
Please enter the next exam: 98
Please enter the next exam: 97
Please enter the next exam: 96
The total sum for all 4 exams is 394
The average for the exams entered is 98.50.
This would be correct except for the last print out of: 'Please enter the next exam: 96'
I tried putting the IF statement between the 'sum' line and the TextIO.put 'Enter next exam', but that isolates it.
Thanks, from a Network Dude trap in a Programmer's world.

You have what is called an off-by-one error, compounded by the fact that you're convoluting your loop logic unnecessarily.
With regards to the loop, I recommend two things:
Don't loop for (int i = 1; i <= N; i++); it's atypical
Do for (int i = 0; i < N; i++); it's more typical
Instead of checking for the last iteration to do something, refactor and take it outside of the loop
Related questions
What is exactly the off-by-one errors in the while loop?
See also
Wikipedia/Off-by-one error
On Double Avg
In Java, variable names start with lowercase. Moreover, Double is a reference type, the box for the primitive double. Whenever possible, you should prefer double to Double
See also
Java Language Guide/Autoboxing
JLS 5.1.7 Boxing Conversion and 5.1.8 Unboxing Conversion
Effective Java 2nd Edition, Item 49: Prefer primitives to boxed primitives
Related questions
What is the difference between an int and an Integer in Java/C#?
Java: What’s the difference between autoboxing and casting?
Why does int num = Integer.getInteger(“123”) throw NullPointerException?
Why does autoboxing in Java allow me to have 3 possible values for a boolean?
Is it guaranteed that new Integer(i) == i in Java? (YES!!!)
When comparing two Integers in Java does auto-unboxing occur? (NO!!!)
Java noob: generics over objects only? (yes, unfortunately)
Rewrite
Here's a way to rewrite the code that makes it more readable. I used java.util.Scanner since I don't think TextIO is standard, but the essence remains the same.
import java.util.*;
public class ExamsFor4 {
public static void main(String[] arguments) {
Scanner sc = new Scanner(System.in);
final int NUM_EXAMS = 4;
int sum = 0;
for (int i = 0; i < NUM_EXAMS; i++) {
System.out.printf("Please enter the %s exam: ",
(i == 0) ? "first" : "next"
);
sum += sc.nextInt();
}
System.out.printf("Total is %d%n", sum);
System.out.printf("Average is %1.2f%n", ((double) sum) / NUM_EXAMS);
}
}
An example session is as follows:
Please enter the first exam: 4
Please enter the next exam: 5
Please enter the next exam: 7
Please enter the next exam: 9
Total is 25
Average is 6.25
Note that:
Only necessary variables are declared
The loop index is local only to the loop
There are no cluttering comments
Instead, focus on writing clear, concise, readable code
If it makes sense to make something final, do so
Constants in Java is all uppercase
Related questions
Why does (360 / 24) / 60 = 0 in Java
Because it performs integer division. This is why the cast to (double) prior to the division in above code is necessary, so that it performs floating point division.
How does the ternary operator work?
This is the ?: operator in above code, also known as the conditional operator.
See also: JLS 15.25 Conditional Operator ?:

Change your end condition to be strictly less than 4 and put the code that prints out the total and average outside the loop.

You should probably put the if-statment outside the for-loop. That way you don't need the if-statement. Second the statement in the loop should be < 4 instead of <= 4.
public class ExamsFor4 {
public static void main(String[] arguments) {
int inputNumber; // One of the exams input by the user.
int sum = 0; // The sum of the exams.
int i; // Number of exams.
Double Avg; // The average of the exams.
TextIO.put("Please enter the first exam: "); // get the first exam.
inputNumber = TextIO.getlnInt();
for ( i = 1; i < 4; i++ ) {
sum += inputNumber; // Add inputNumber to running sum.
TextIO.put("Please enter the next exam: "); // get the next exam.
inputNumber = TextIO.getlnInt();
}
Avg = ((double)sum) / i;
TextIO.putln();
TextIO.putln("The total sum for all " + i +" exams is " + sum);
TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);
break;
} // end main ()
}

Just making few changes in your code makes it work. But you should follow cleaner approach as proposed in some of answers.
public class ExamsFor4 {
public static void main(String[] arguments) {
int inputNumber; // One of the exams input by the user.
int sum = 0; // The sum of the exams.
int i; // Number of exams.
double Avg; // The average of the exams.
TextIO.put("Please enter the first exam: "); // get the first exam.
inputNumber = TextIO.getlnInt();
sum += inputNumber;
for ( i = 1; i < 4; i++ ) {
TextIO.put("Please enter the next exam: "); // get the next exam.
inputNumber = TextIO.getlnInt();
sum += inputNumber; // Add inputNumber to running sum.
}
Avg = ((double)sum) / i;
TextIO.putln();
TextIO.putln("The total sum for all " + i +" exams is " + sum);
TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);
} // end main ()
} // end class ExamsFor4

import java.util.Scanner;
public class ExamsFor4 {
public static void main(String[] arguments) {
int sum = 0; // The sum of the exams.
int i = 1; // Number of exams.
double avg = 0; // The average of the exams.
Scanner in = new Scanner(System.in);
System.out.print("Please enter the first exam: ");
sum += in.nextInt();
i++;
while(i<=4){
System.out.print("Please enter the next exam: ");
sum += in.nextInt();
if(i==4)
break;// this line is so that it wont increment an extra time.
i++;
}
System.out.println("The total sum for all " + i +" exams is " + sum);
avg = ((double)sum/i);
System.out.println("The average for the exams entered is" + avg);
} // end main ()
} // end class ExamsFor4