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How to divide variables in java for a GPA calculator

I'm currently working on a GPA calculator for a class of mine. I keep getting an error that has to do with the division I'm trying to do on the GPA calculation and am having trouble with the syntax for sub-strings and how to use them correctly. Below is the code I have so far. If you see anything I can fix that's not to complicated I'm open to all suggestions.
import java.util.Scanner;
public class GPA
{
public static void main(String[] mydata)
{
Scanner sc = new Scanner(System.in);
String choice = "";
String cnum;
String grade;
double points;
double gpa = 0;
int count = 0;
String credit= "", totalCredit = "";
while (!choice.equalsIgnoreCase("Q"))
{
cnum = (mydata[0]);
grade = (mydata[1]);
if (grade.equalsIgnoreCase("A")) {points = 4.0;}
else if (grade.equalsIgnoreCase("B")) {points = 3.0;}
else if (grade.equalsIgnoreCase("C")) {points = 2.0;}
else if (grade.equalsIgnoreCase("D")) {points = 1.0;}
else if (grade.equalsIgnoreCase("F")) {points = 0.0;}
credit = cnum.substring(3,4);
//System.out.println("credits = " + totalCredit);
System.out.println("GPA = " points/Double.parseDouble(credit));
System.out.print("Enter next course number and grade or ‘Q’ to quit: ");
System.out.println();
choice = sc.nextLine();
}
System.out.println("Bye!");
}
}

Not bad but there are a couple syntactical errors with your code:
The println argument needs to be concatenated with a +:
System.out.println("GPA = " + points / Double.parseDouble(credit));
The local variable, points, needs to be initialized since your if-else conditions are not exhaustive (ie: grade has a runtime range of A, B, C, D, or F but grade can technically be assigned to whatever is in mydata[1]). Either add an else condition or assign an initial value to points:
double points = 0.0;

Be sure to include + to concat the strings together :)
System.out.println("GPA = " + (points/Double.parseDouble(credit)));

I believe you want to be concatenating here.
System.out.println("GPA = " + (points/Double.parseDouble(credit)));
Instead of
System.out.println("GPA = " (points/Double.parseDouble(credit)));
And if you want
int theGpa = points/Double.parseDouble(credit));
System.out.println("GPA: " + theGpa);

Counter won't work to end loop [closed]

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I am working on an assignment and it is working well so far. But several aspects aren't working. For starters, my counters for int total and int counter won't work. Also my if statements don't seem to be working. I have been scratching my head for several days now.
The assignment calls for a program to input the order number and will loop based on how many orders the customer has. It also calls for customer name, sign type(wood or plastic), the number of characters,and color of characters.
Some more information:
The base price for all signs is $20.
If sign is wood, add $10. If it is plastic add $5.
The first 5 letters/numbers are included in base price, and $2 for each additional character.
Black or white characters are included in base price, there is an additional $8 for colored letters.
If the total charge is more than $100 give 25% discount on total price.
Here is my code right now:
import java.util.Scanner;
public class Carpenter {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int orderNumber;
String custName;
String signType;
int numOfCharacters;
String color;
int i = 20;
double total;
int counter;
System.out.println("Enter your order number");
orderNumber = sc.nextInt();
counter=orderNumber;
counter--;
sc.nextLine();
System.out.println("Enter customer name");
custName = sc.next();
do{
System.out.println("Enter the sign type (wood or plastic)");
signType = sc.next();
if(signType == "wood") {
i+=10;
}
if(signType == "plastic") {
i+=5;
}
System.out.println("Enter the number of characters");
numOfCharacters = sc.nextInt();
if(numOfCharacters > 5) {
i += 2*(numOfCharacters-5);
}
System.out.println("Enter the color of characters");
color = sc.next();
if(color != "white" || color != "black") {
i += 8;
}
total= i;
System.out.println("Total is: $" + total);
if( total > 100 ) {
total = (total * 0.25);
System.out.println("The total is " + total );
}
}
while(counter <= orderNumber);
}
}

I added comments to guide you through the changes I made. Also, remember to call the sc.NextLine() function after you get user input so that they can input something different next time (this is called 'flushing' the buffer).
import java.util.Scanner;
public class Carpenter {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int orderNumber;
String custName;
String signType;
int numOfCharacters;
String color;
int i = 20;
double total;
int counter;
//I changed the phrasing just because it is a little confusing
System.out.println("Enter your number of orders");
orderNumber = sc.nextInt();
counter = orderNumber;
sc.nextLine();
System.out.println("Enter customer name");
custName = sc.next();
sc.nextLine();
//When you know how many times you want to repeat something (like when a user tells you how many) I prefer using a for-loop, a do while loop works as well though
for(int x=0; x<counter;x++)
{
System.out.println("Enter the sign type (wood or plastic)");
signType = sc.next();
//When comparing Strings, there is a function that you can use to compare them rather than using '=='
// It is also good to use the 'equalsIgnoreCase()' function to be more user friendly and robust
if(signType.equalsIgnoreCase("wood")) {
i+=10;
}
if(signType.equalsIgnoreCase("plastic")) {
i+=5;
}
//Flush the buffer (I haven't tested if this is necessary or not, it is good practice though)
sc.nextLine();
System.out.println("Enter the number of characters");
numOfCharacters = sc.nextInt();
if(numOfCharacters > 5) {
i += 2*(numOfCharacters-5);
}
System.out.println("Enter the color of characters");
color = sc.next();
//Same concept as above, the differene is the ! before the function to test if it is false or not
if(!color.equalsIgnoreCase("white") || !color.equalsIgnoreCase("black")) {
i += 8;
}
}
total = i;
//You will not want to print this out until the end due to the possibility of it being over $100
// System.out.println("Total is: $" + total);
if( total > 100 ) {
//Mathematically speaking, you are making your total a quarter of what the original is, rather than taking a quarter off. You want 75% rather than 25%
// total = (total * 0.25);
total = (total * 0.75);
}
System.out.println("Total is: $" + total);
}
}

You should set counter to the correct starting value (which is presumably 1 in your case):
orderNumber = sc.nextInt();
counter=1;
//counter=orderNumber;
//counter--;
Then at the end of the loop, you should increment your counter:
do{
//code
counter++;
}
while(counter <= orderNumber);

Java Interests loop with method

I have a method which calulates intrests.
public static float calculateIntrests (float Principal, float RateInPercentage){
float result;
result=Principal*RateInPercentage;
return result;
Now I need a loop to print me how much "money" do I have each year. I have done something like this.
import java.util.Scanner;
public class Aplikacija {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int years = 1;
System.out.println("Principal!");
float Principal = input.nextInt();
System.out.println("Rate!");
int Rate = input.nextInt();
float RateInPercentage = Rate / 100.0f;
float calculate = Caluclateintrests(Principal, rateinPercentage);
while (year <= 5) {
System.out.println("It is: " + (calculate) + " dollars in year" + year + "on your account");
year++;
}
input.close();
}
}

Java is a case sensitive, so if you declared variable, method or class with a specific name then you have to sick with the declared name in order to use it,
So you have declared years but you used year instead
int years = 1;
But used as:
while (year <= 5) {//
So here you can do two of thins:
change the declaration of years to be year.
change the using of that variable to years.
This also goes with RateInPercentage variable, Caluclateintrests method.

You have lots and lots of mistakes. Remember to spell it right and that Java is case-sensitive, therefore you have to keep eye on capital letters.
And few mistakes are not syntax, but in logical matter.
Also the naming convention for Java suppose to start naming variables and methods with lower-case letter.
This is working code, try to learn from it :
import java.util.Scanner;
public class Aplikacija {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int year = 1;
System.out.println("Principal!");
float principal = input.nextInt();
System.out.println("Rate!");
int rate = input.nextInt();
float rateInPercentage = rate / 100.0f;
while (year <= 5) {
principal += calculateIntrests(principal, rateInPercentage);
System.out.println("It is: " + principal + " dollars in year" + year + " on your account");
year++;
}
input.close();
}
public static float calculateIntrests(float principal, float rateInPercentage) {
float result;
result = principal * rateInPercentage;
return result;
}
}
Sample output :
Principal!
100
Rate!
1
It is: 101.0 dollars in year1 on your account
It is: 102.01 dollars in year2 on your account
It is: 103.030106 dollars in year3 on your account
It is: 104.06041 dollars in year4 on your account
It is: 105.10101 dollars in year5 on your account

Looping with different variables?

Before this the user inputs an int for numOfTimes. Say it's 5. This will ask the question 5 times. But each time through it will erase the previous value in hrs1. It needs to be a separate variable. So if numOfTimes=5 Then I should get 5 different doubles for "Hour " and 5 different doubles for "Minute ". (assuming the user inputs different times) but they all need to be stored in different variables. How should I do this?
Thank you my question has been answered!

use an array ..
int a[] = new int[5];
for(int i =0;i<5;i++){
a[i] = //your value
}

You just need to put your "calculate average" code outside the for loop. I am not sure exactly how you want to calculate the average. But here are two simple ways.
Method one - keep track of the totals and calculate the basic average.
public class AvgTime {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("How many times? ");
int numOfTimes = in.nextInt();
System.out.println("\n");
double hrTotal = 0;
double minTotal = 0;
for (int i = 1; i <= numOfTimes; i++){
System.out.println("What Time (military time): ");
System.out.print("Hour ");
double hrs1 = in.nextDouble();
System.out.print("Minute ");
double min1 = in.nextDouble();
hrTotal += hrs1;
minTotal += min1;
}
//calculate average
double avdHr1 = hrTotal/numOfTimes;
double timeMin1 = minTotal/numOfTimes;
System.out.println(avgHr1+":"+timeMin1 + " P.M");
}
}
Method 2 - Use lists and iterate twice
public class AvgTime {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("How many times? ");
int numOfTimes = in.nextInt();
System.out.println("\n");
ArrayList<Double> hours = new ArrayList<>();
ArrayList<Double> minutes = new ArrayList<>();
double minTotal = 0;
for (int i = 1; i <= numOfTimes; i++){
System.out.println("What Time (military time): ");
System.out.print("Hour ");
double hrs1 = in.nextDouble();
System.out.print("Minute ");
double min1 = in.nextDouble();
hours.add(hrs1);
minutes.add(min1);
}
//calculate average
double avgHr1 = 0;
double timeMin1 = 0:
for (int i = 0; i < hours.size(); i++) {
double hour = hours.get(i);
double minute = minutes.get(i);
//ToDo: calculate average so far
}
System.out.println(avgHr1+":"+timeMin1 + " P.M");
}

You can use arrays to store the information the user has input. Before the loop, make an array using the new keyword, e.g. double[] hrs=new double[numOfTimes]. In the loop, write to different locations in the array for each input, hrs[i]=in.nextDouble(). You can later read from a position on the array using the syntax 'name[index]', such as 'hrs[2]'. Note that for java and many other languages, arrays start at 0. This means for an array [1,2,3] named arr, arr[1] equals 2 instead of 1. This means it would be best if your for loop was changed from for(int i=1;i<=numofTimes;i++) to 'for(int i=0;i

<SOAPBOX,RANT,HIGHHORSE>
This is more of a code review than a straight answer, but something has been bugging me about newbie questions that I've observed on stackoverrflow.
When developing, I avoid keyboard input like the plague. It is such drudgery, especially with a loop such as in this program. So many newbie questions have user-keyboard input. Why?! It makes development so much more difficult!
I've rewritten your program to add the ability for testing data, completely avoiding the need for user-input during development. When testing is over, just switch the test/live comments around.
I'm sure there's a more elegant way, but this style has worked well for me, and I recommend it.
</SOAPBOX,RANT,HIGHHORSE>
import java.util.*;
import static java.lang.Math.abs;
public class AverageTimeWTestingData {
public static void main(String[] args) {
HourMin24[] ahm = null;
//EXACTLY ONE of the following lines must be commented out
//Test only:
ahm = getTestData();
//Live only:
// ahm = getDataFromUserInput();
double dTotalHours = 0.0;
for (HourMin24 hm : ahm){
System.out.println("Time: " + hm.iHour + ":" + hm.iMin);
dTotalHours += hm.iHour + (hm.iMin / 60);
}
System.out.println("Average time (" + ahm.length + "): " + (dTotalHours / ahm.length));
}
private static final HourMin24[] getDataFromUserInput() {
Scanner in = new Scanner(System.in);
System.out.print("How many times? ");
int numOfTimes = in.nextInt();
ArrayList<HourMin24> al24 = new ArrayList<HourMin24>(numOfTimes);
while(numOfTimes < 0) {
System.out.println("What Time (military time): ");
System.out.print("Hour ");
int iHour = in.nextInt();
System.out.print("Minute ");
int iMin = in.nextInt();
al24.add(new HourMin24(iHour, iMin));
numOfTimes--;
}
return al24.toArray(new HourMin24[al24.size()]);
}
private static final HourMin24[] getTestData() {
System.out.println("TEST MODE ON");
return new HourMin24[] {
new HourMin24(13, 1),
new HourMin24(23, 19),
new HourMin24(0, 59),
new HourMin24(16, 16),
};
}
}
class HourMin24 {
public int iHour;
public int iMin;
public HourMin24(int i_hour, int i_min) {
iHour = i_hour;
iMin = i_min;
}
}
Output:
[C:\java_code\]java AverageTimeWTestingData
TEST MODE ON
Time: 13:1
Time: 23:19
Time: 0:59
Time: 16:16
Average time (4): 13.0

Java loan calculator

I'm trying to code a loan calculator. I seem to be having issues. I am trying to get an input from the user and validate the input. I know I am doing it wrong the problem is I'm scratching my head wondering how to do it right.
I get a red line on the d = getDouble(sc, prompt); and the i = getInt(sc, prompt); which I understand I don't have that coded correctly. I'm just unsure how to go about fixing it.
I also have to validate the continue statement which I wasn't to sure the best way to go about that and finally the instructor expects the code to be 80 lines or less which I am right about 80 lines. I guess I'm looking for a better way to do this but being new I'm scratching my head and I'm hoping someone can lend a hand.
As always I really appreciate the help.
import java.util.Scanner;
import java.text.NumberFormat;
public class LoanCalculator
{
public static double getDoubleWithinRange(Scanner sc, String prompt, double min, double max)
{
double d = 0.0;
boolean isValid = false;
while(isValid == false);
{
d = getDouble(sc, prompt);
if (d <= min)
{
System.out.println("Error! Number must be greater tha 0.0");
}
else if (d >= max)
{
System.out.println("Error number must be less than 1000000.0");
}
else
isValid = true;
}
return d;
}
public static int getIntWithinRange(Scanner sc, String prompt, int min, int max)
{
int i = 0;
boolean isvalid = false;
while(isvalid == false)
{
i = getInt(sc, prompt);
if (i <= min)
System.out.println("Error! Number must be more than 0");
else if (i >= max)
System.out.println("Error! Number must be less than 100");
else
isvalid = true;
}
}
public static void main(String[] args)
{
System.out.println("Welcome to the loan calculator");
Scanner sc = new Scanner(System.in);
String choice = "y";
while (choice.equalsIgnoreCase("y"))
{
System.out.println("DATA ENTRY");
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ", 0.0, 1000000.0);
double interestRate = getDoubleWithinRange(sc, "Enter yearly interest rate: ", 0, 20);
int years = getIntWithinRange(sc, "Enter number of years: ", 0, 100);
int months = years * 12;
double monthlyPayment = loanAmount * interestRate/
(1 - 1/Math.pow(1 + interestRate, months));
NumberFormat currency = NumberFormat.getCurrencyInstance();
NumberFormat percent = NumberFormat.getPercentInstance();
percent.setMaximumFractionDigits(3);
System.out.println("RESULST");
System.out.println("Loan Amount" + currency.format(loanAmount));
System.out.println("Yearly interest rate: " + percent.format(interestRate));
System.out.println("Number of years: " + years);
System.out.println("Monthly payment: " + currency.format(monthlyPayment));
System.out.println();
System.out.println("Continue? (y/n): ");
choice =sc.next();
System.out.println();
}
}
}

You haven't made the implementation of your getDouble(Scanner,String) and getInt(Scanner,String) that's why you're getting the red line.
since you already have a scanner, and prompt string change it to this
System.out.print(prompt);
d = sc.nextDouble();
and for the integer
System.out.print(prompt);
i = sc.nextInt();

I think getDouble and getInt are string functions so you would have to get a string first then call those methods. However, since you have a scanner, I assume you want to use that with the nextXXX methods:
Scanner sc = new Scanner (System.in);
double d = sc.nextDouble();
You can use this complete snippet for educational purposes:
import java.util.Scanner;
class Test {
public static void main (String args[]) {
Scanner sc = new Scanner (System.in);
System.out.print("Enter your double: ");
double d = sc.nextDouble();
System.out.print("Enter your integer: ");
int i = sc.nextInt();
System.out.println("You entered: " + d + " and " + i);
}
}
Transcript:
Enter your double: 3.14159
Enter your integer: 42
You entered: 3.14159 and 42
Basically, the process is:
Instantiate a scanner, using the standard input stream.
Use print for your prompts.
Use the scanner nextXXX methods for getting the input values.
A little more assistance here, based on your comments.
In your main function, you have:
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ", 0.0, 1000000.0)
and that function has the prototype:
public static double getDoubleWithinRange(
Scanner sc, String prompt, double min, double max)
That means those variables in the prototype will be set to the values from the call. So, to prompt for the information, you could use something like (and this is to replace the d = getDouble(sc, prompt); line):
System.out.print(prompt);
double d = sc.nextDouble();
And there you have it, you've prompted the user and input the double from them. The first line prints out the prompt, the second uses the scanner to get the input from the user.
As an aside, your checks for the minimum and maximum are good but your error messages have hard-coded values of 0 and 100K. I would suggest that you use the parameters to tailor these messages, such as changing:
System.out.println("Error! Number must be greater tha 0.0");
into:
System.out.println("Error! Number must be greater than " + min);
That way, if min or max change in future , your users won't get confused :-)
I'll leave it up to you to do a similar thing for the integer input. It is your homework, after all :-)