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My program runs but I'm getting an error String index out of range: 3 When I enter 1 2 for example. I tried changing the values of 1 in partStr = str.substring(lastSpace + 1, x); but that didn't work. Any ideas what I'm doing wrong?
public static void main(String[] args) {
String str;
int x;
int length;
int start;
int num;
int lastSpace = -1;
int sum = 0;
String partStr;
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter a series of integers separated by spaces >> ");
str = keyboard.nextLine();
length = str.length();
for (x = 0; x <= length; x++) {
if (str.charAt(x) == ' ') {
partStr = str.substring(lastSpace + 1, x);
num = Integer.parseInt(partStr);
System.out.println(" " + num);
sum += num;
lastSpace = x;
}
}
partStr = str.substring(lastSpace + 1, length);
num = Integer.parseInt(partStr);
System.out.println(" " + num);
sum += num;
System.out.println(" -------------------" + "\nThe sum of the integers is " + sum);
}
You should traverse upto length - 1.
The indexing in String is similar to what happens in arrays.If the length of String is 5 for example,the characters are stored in 0-4 index positions.
Your current loop is traversing beyond the size of the string.
str.length() will return the amount of characters of the string, let's say N
for(x = 0; x <= length; x++) will loop N+1 times, instead of N, because the index starts at 0 and you also enter the loop when x is equal to the length
replacing <= with < in the for loop will fix your problem
The issue you faced is because you tried to access a character at the index, x (i.e. str.charAt(x)) from str where x is beyond the maximum value of the index in str. The maximum value of the index in str is str.length - 1 whereas the for loop is running up to str.length. In order to fix that problem, you need to change the condition to x < length.
However, even after fixing that issue, your program may fail if any entry is non-integer or if there are multiple spaces in the input. A clean way, including exception handling, to do it would be as follows:
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
String str;
int sum = 0;
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter a series of integers separated by spaces >> ");
str = keyboard.nextLine();
// Split str on space(s) and assign the resulting array to partStr
String[] partStr = str.split("\\s+");
// Iterate through partStr[] and add each number to sum
for (String num : partStr) {
try {
sum += Integer.parseInt(num);
} catch (NumberFormatException e) {
// Integer::parseInt will throw NumberFormatException for a non-integer string.
// Display an error message for such entries.
System.out.println(num + " is an invalid entry");
}
}
// Display the entries and the sum
System.out.println("Your entries are: " + Arrays.toString(partStr));
System.out.println("The sum of the integers is " + sum);
}
}
A sample run:
Enter a series of integers separated by spaces >> 10 a 20 10.5 30 b xy 40
a is an invalid entry
10.5 is an invalid entry
b is an invalid entry
xy is an invalid entry
Your entries are: [10, a, 20, 10.5, 30, b, xy, 40]
The sum of the integers is 100
I am working on an array problem for my college course and I'm trying to find the sum and the average of an array. Here's the code I have so far.
public class Module55
{
public static void main(String args[])
{
//declare the array to have 10 items for 10 weeks
//also declare sum as an int and average as a double to accommodate for decimal points
int[] weeks = new int[10];
int sum = 0;
double average = 0;
//declare the array values
weeks[0]= 2;
weeks[1]= 4;
weeks[2]= 8;
weeks[3]= 10;
weeks[4]= 14;
weeks[5]= 16;
weeks[6]= 20;
weeks[7]= 22;
weeks[8]= 24;
weeks[9]= 26;
// determine sum of the array values
for (int index = 0; index < weeks.length; index++) weeks[index] = index;
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);
// determine the average of the array values
if (weeks.length != 0)
average = sum / weeks.length;
else
average = 0;
System.out.println("The average of the miles ran in 10 weeks is " + average);
}
}
I know that the average works but I'm stuck on the sum. The problem I'm having is I cant seem to initialize the values in the array so that I can provide a sum for them. What am I doing wrong or what am I missing?
You have two problems in your code;
A) For-loop assignment
You don't need to make the first assignment, just adding sum to the week[index] is ok;
for (int index = 0; index < weeks.length; index++)
sum = sum + weeks[index];
B) Calculating the average
Sum is defined as an int which is a primitive integer, because of that, the division of an integer to an integer, the output is an integer which is not precise. Output of the division (45/10) is casted to integer, then assigned to double which is rounded off to 4, then casted to double again, and '4.0' became the result.
To avoid this unprecise result, cast sum to the double as below;
average = (double)sum / weeks.length;
The corrected version of your code is as below;
Demo
public class Module55 {
public static void main(String args[]) {
// declare the array to have 10 items for 10 weeks
// also declare sum as an int and average as a double to accommodate for
// decimal points
int[] weeks = new int[10];
int sum = 0;
double average = 0;
// declare the array values
weeks[0] = 2;
weeks[1] = 4;
weeks[2] = 8;
weeks[3] = 10;
weeks[4] = 14;
weeks[5] = 16;
weeks[6] = 20;
weeks[7] = 22;
weeks[8] = 24;
weeks[9] = 26;
// determine sum of the array values
for (int index = 0; index < weeks.length; index++)
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);
// determine the average of the array values
if (weeks.length != 0)
average = (double)sum / weeks.length;
else
average = 0;
System.out.println("The average of the miles ran in 10 weeks is " + average);
}
}
Output
The total miles ran in 10 weeks is 146
The average of the miles ran in 10 weeks is 14.6
And a note for scope
And one last note about the scope, check out this code;
for (int index = 0; index < weeks.length; index++)
weeks[index] = index;
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);
In the for-loop, because that no brackets are used, only the first statement under the for-loop will be considered in the scope of the loop by the compiler. That's why, for the next line, the compiler is giving error about the index because index is defined inside the scope of the for-loop.
you need to use brackets in your for loop. currently your code is evaluating like this:
for (int index = 0; index < weeks.length; index++)
{
weeks[index] = index;
}
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);
you want your code to evaluate like this
for (int index = 0; index < weeks.length; index++)
{
weeks[index] = index; //logical issue, what does this line achieve?
sum = sum + weeks[index];
}
System.out.println("The total miles ran in 10 weeks is " + sum);
This will at least solve your procedural problems but you will still need to take a look at your logic. Try using breakpoints to debug your code.
A very simple way to achieve this in Java 8 is to use the built in mechanisms for gathering statistics:
int[] weeks = {3, 4, 6, 9, 10};
IntSummaryStatistics stats = IntStream.of(weeks).summaryStatistics();
System.out.println("sum = " + stats.getSum() + "; average = " + stats.getAverage());
for (int i = 0;i < weeks.length) {
sum += weeks[i];
}
System.out.println("Sum is:" + sum);
First of all, you simply don't need the line weeks[index] = index;.
And for average you have to cast the sum to double if you want to get the average in double as you have declared the sum as int.
public class Module55
{
public static void main(String args[])
{
//declare the array to have 10 items for 10 weeks
//also declare sum as an int and average as a double to accommodate for decimal points
int[] weeks = {2,4,8,10,14,16,20,22,24,26};
int sum = 0;
double average = 0;
// determine sum of the array values
for (int index = 0; index < weeks.length; index++)
//weeks[index] = index;
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);
// determine the average of the array values
if (weeks.length != 0)
average = (double)sum / weeks.length;
else
average = 0;
System.out.println("The average of the miles ran in 10 weeks is " + average);
}
}
The total miles ran in 10 weeks is 146
The average of the miles ran in 10 weeks is 14.6
Summing an array of numbers and dividing by n to get the average like this will not get the correct value - you should not compute the average using integer division.
Also, this approach might work for the example shown, but not in general. For example, try using this code to find the average of these two value: (INT_MAX-6) and (INT_MAX-2).
The corrected code. While calculating average you have cast on of the varibale to double else you will get the average as integer
public class Mod55 {
public static void main(String args[]) {
//declare the array to have 10 items for 10 weeks
//also declare sum as an int and average as a double to accommodate for decimal points
int[] weeks = new int[]{2, 4, 8, 10, 14, 16, 20, 22, 24, 26};
int sum = 0;
double average = 0;
// determine sum of the array values
for (int index = 0; index < weeks.length; index++) {
sum += weeks[index];
}
System.out.println("The total miles ran in 10 weeks is " + sum);
// determine the average of the array values
if (weeks.length != 0) {
average = (double)sum / weeks.length;
} else {
average = 0;
}
System.out.println("The average of the miles ran in 10 weeks is " + average);
}
}
Java8 You could achieve the same thing like this.
int[] weeks = new int[]{2, 4, 8, 10, 14, 16, 20, 22, 24, 26};
int sum = Arrays.stream(weeks)
.sum();
double average = Arrays.stream(weeks).average().orElse(0);
you can find this handy with lambdas.The code looks something like this.
int weeks[] = {1,2,3,4};
List<Integer> asd = IntStream.of(weeks).boxed().collect(Collectors.toList());
//asd.forEach(System.out::println);
//this outputs average
System.out.println(asd.stream().mapToDouble(val -> val).sum()/asd.size());
//this outputs sum
System.out.println(asd.stream().mapToInt(val -> val).sum());
//another way to achieve this thanks to commenter
System.out.println(IntStream.of(asd).summaryStatistics());
I am writing a program that reads a sequence of positive integers input by the user. User will only enter one integer at a time.Then it will compute the average of those integers. The program will end when user enters 0. (0 is not counted in the average).The program will print out the average once the program ends.
Question: My code stops working when I gets to the while loop hence it doesn't compute the input by user, hence prints out nothing. Why doesn't my while loop compute the average from the user's inputs? Appreciate your guidance :)
import java.util.Scanner;
public class AverageOfIntegers {
public static void main(String[] args) {
int integer;
double sum;
sum = 0;
double average;
Scanner input = new Scanner(System.in);
int count; count = 0;
average = 0;
System.out.println("Please enter an integer: ");
integer = input.nextInt();
while (integer != 0) {
count = count + 1;
sum = sum + integer;
average = sum / count;
}
System.out.println("Average = " + average);
}
}
This is because you are never actually summing over more than one integer. The user only ever enters one number. As a result your loop is essentially acting on just the one number. You need to put the input inside the while loop and save a running sum and count there. Something more like this
while (integer != 0) {
count += 1;
sum += integer;
average = sum / count;
integer = input.nextInt();
}
Explanation
First of all, when you define data types, you can set their default value in the definition. Ex:
double sum = 0;
vs
double sum;
sum = 0;
Secondly, sum = sum + integer; is the same as: sum += integer;
Thirdly, count = count + 1; is the same as: count += 1 OR (and better yet), count++;
As for your actual algorithm, there is one problem and one suggestion:
you are not changing integer's value after each loop. So, you can
either do that in the while condition: while ((integer =
input.nextInt()) != 0) { or, at the end of each loop:
while (integer != 0) {
count ++;
sum += integer;
average = sum / count;
integer = input.nextInt();
}
This is a suggestion for technically better code (in my opinion), but it looks better, is more intuitive and requires less calculations to calculate the average after the while loop is done instead of during. That way, you only calculate it once, where needed, vs. every loop, which is not needed.
________________________________________________________________________________
The Code (complete class)
public class AverageOfIntegers {
public static void main(String[] args) {
int integer;
double sum = 0;
double average = 0;
Scanner input = new Scanner(System.in);
int count = 0;
System.out.println("Please enter an integer: ");
// set integer = to the nextInt() while looping so it calculates properly
while ((integer = input.nextInt()) != 0) {
count ++;
sum += integer;
}
average = sum / count; // calculate the average after the while-loop
System.out.println("Average = " + average);
}
}
________________________________________________________________________________
Example input/output:
Please enter an integer:
5
10
15
0
Average = 10.0
So it did 5 + 10 + 15 = 30 (which is the sum), and then the average is 30 / 3 (30 is the sum, 3 is the count), and that gave you Average = 10.0.
You need to move integer = input.nextInt(); inside the loop, so your program will collect inputs in a loop. See the corrected version:
import java.util.Scanner;
public class AverageOfIntegers {
public static void main(String[] args) {
int integer = 0, count = 0;
double sum = 0.0, average = 0.0;
Scanner input = new Scanner(System.in);
System.out.println("Please enter an integer: ");
integer = input.nextInt();
while (integer != 0) {
count = count + 1;
sum = sum + integer;
System.out.println("Please enter an integer: ");
integer = input.nextInt();
}
average = sum / count;
System.out.println("Average = " + average);
}
}
The problem is that the input.nextInt() should be part of the loop. The way you wrote it, the code gooes into an infinite loop whenever the first input is non-zero. Instead, do:
while ((integer = input.nextInt()) != 0) {
count = count + 1;
sum = sum + integer;
average = sum / count;
}
In the loop:
while (integer != 0) {
count = count + 1;
sum = sum + integer;
average = sum / count;
}
This will only stops when integer is 0, but this variable is not changing in the loop, so it will never be 0 if it wasn't already in the first place.
According to what you said you want to do, you should probably repeat the call to integer = input.nextInt(); inside your loop, lke this:
System.out.println("Please enter an integer: ");
integer = input.nextInt();
while (integer != 0) {
count = count + 1;
sum = sum + integer;
System.out.println("Please enter an integer: ");
integer = input.nextInt();
}
average = sum / count;
Also, as others have said, you only need to compute the average once after the loop, so I moved it too.
This question already has answers here:
How do I get this code to stop input when the sum exceeds 100 and still preform the sum and average?
(2 answers)
Closed 9 years ago.
When I run this code and input numbers whose sum>100 the output is correct for the count and the sum but the average is wrong. For example; input 8,10,99... the count is 3, the sum is 117 and should return an average of 39... the actual output returned is count 3, sum 117 and average 58.5. I have come to realize this is because the average is being done using a count of 2 instead of 3(or always one less than it should be with different values). Why is this? It works perfect for inputs sum<=100. PLEASE HELP :)
public static void main(String[] args) {
//Use Main Method for gathering input
float input = 1;
// Declare variable for sum
float theSum = 0;
// Declare variable for average
float average = 0;
// Declare variable for counting the number of user inputs
int counter = 0;
/* Initialize the while loop using an input of 0 as a sentinel value
* to exit the loop*/
while (input != 0) {
// Use JOptionPane method to accept input from user
input = Float.parseFloat(
JOptionPane.showInputDialog(
null, "Please enter a number. Enter 0 to quit: "));
// Invoke sum method and pass input and summation to sum method
theSum = (sum(input, theSum));
// Invoke avg method and pass summation and counter to avg
average = (avg(theSum, counter));
// Increment the counter variable
counter++;
if (theSum > 100)
{
JOptionPane.showMessageDialog(null, "The sum of your numbers "
+ "are greater than 100!");
break;
}
}
// Invoke display method and pass summation, average, and counter variables to it
display(theSum, average, counter);
}
public static float sum(float num1, float sum) {
//Add the user's input number to the sum variable
sum += num1;
//Return value of sum variable as new summation variable
return sum;
}
public static float avg(float num1, int num2) {
//Declare and initialize variable for average
float average = 0;
//Calculate average
average = num1 / num2;
//Return value of average variable
return average;
}
public static void display(float sum, float average, int counter) {
/* I am subtracting 1 from variable counter so as not to include the sentinel value
* of 0 that the user had to enter to exit the input loop in the overall count*/
// Display the count, sum, and average to the user
if (sum > 100) {
JOptionPane.showMessageDialog(null, "Count = " + (counter) + ", Sum = " + sum + ", Average = " + average);
}
if (sum <= 100) {
JOptionPane.showMessageDialog(null, "Count = " + (counter - 1) + ", Sum = " + sum + ", Average = " + average);
}
}
}
You increment the counter after taking average, which is why you see your average based on 2 numbers rather than your expected 3.
average = (avg(theSum, counter));
// Increment the counter variable
counter++;
Swap those two and increment counter before you take average.
counter++;
// Increment the counter variable
average = (avg(theSum, counter));
Edit:
Here is what you should change:
First, update the counter only if input is not = 0
if(input!=0)
{
counter++;
}
Secondly, move the average code out of the loop and it put it in the end just before display, don't need to compute average again and again.
average = (avg(theSum, counter));
display(theSum, average, counter);
Thirdly, remove counter-1 from display method and print counter
public static void display(float sum, float average, int counter) {
JOptionPane.showMessageDialog(null, "Count = " + (counter) + ", Sum = " + sum + ", Average = " + average);
}
After that, it works for both cases like you expect
This question already has answers here:
How do I get this code to stop input when the sum exceeds 100 and still preform the sum and average?
(2 answers)
Closed 9 years ago.
Yes, I know there are a lot of methods here. It's part of the assignment. In this code everything works as intended except that when numbers are entered that equal sum<=100, the "average" output is wrong. For example: if I put in 8,10,19 and zero to exit the output is count 3 sum 37 average 9.25.... the average should be 12.3333. Now, if i enter in 8, 10, 99 the output is count 3 sum 117 and average 39 which is correct. Why is it working for sum>100 but not sum<=100??? I don't get it. What am I missing?
public static void main(String[] args) {
//Use Main Method for gathering input
float input = 1;
// Declare variable for sum
float theSum = 0;
// Declare variable for average
float average = 0;
// Declare variable for counting the number of user inputs
int counter = 0;
/* Initialize the while loop using an input of 0 as a sentinel value
* to exit the loop*/
while (input != 0) {
if (input!=0){
counter++;
}
input = Float.parseFloat(
JOptionPane.showInputDialog(
null, "Please enter a number. Enter 0 to quit: "));
// Invoke sum method and pass input and summation to sum method
theSum = (sum(input, theSum));
if (theSum > 100)
{
JOptionPane.showMessageDialog(null, "The sum of your numbers "
+ "are greater than 100!");
break;
}
}
// Invoke display method and pass summation, average, and counter variables to it
average = (avg(theSum, counter));
display(theSum, average, counter);
}
public static float sum(float num1, float sum) {
//Add the user's input number to the sum variable
sum += num1;
//Return value of sum variable as new summation variable
return sum;
}
public static float avg(float num1, float num2) {
//Declare and initialize variable for average
//Calculate average
float average = num1 / num2;
//Return value of average variable
return average;
}
public static void display(float sum, float average, int counter) {
/* I am subtracting 1 from variable counter so as not to include the sentinel value
* of 0 that the user had to enter to exit the input loop in the overall count*/
// Display the count, sum, and average to the user
if (sum > 100) {
JOptionPane.showMessageDialog(null, "Count = " + (counter) + ", Sum = " + sum + ", Average = " + average);
}
if (sum <= 100) {
JOptionPane.showMessageDialog(null, "Count = " + (counter - 1) + ", Sum = " + sum + ", Average = " + average);
}
}
}
The reason is that you're exiting the while loop in different ways depending on the total sum. If the sum is less than 100, even when you enter the number 0 to "exit", you're still going through the loop an extra time. To be honest, the entire loop needs to be completely restructured; a do...while loop would be much easier to read and debug.
The issue is because of the way you exit the while loop as mentioned by #chrylis. So in case where the sum is <= 100 the counter is 1 larger. But when you print it you get correct result because you update the counter value here:
if (sum <= 100) {
JOptionPane.showMessageDialog(null, "Count = " + (counter - 1) + ", Sum = " + sum + ", Average = " + average);
}
As you see in your example:
"if I put in 8,10,19 and zero to exit the output is count 3 sum 37 average 9.25"
it is because the counter value is 4 (so the avg will be 37/4 = 9.25), but while displaying the result you subtract counter by 1, therefore you get the count as 3.
The do-while loop will solve the issue as the condition would be checked at the last thus the loop will exit in same manner for both <=100 and '>100`.
The do-while loop would be like this:
do{
//here goes your code
}while (input != 0);
Your counter is 1 larger than necessary. Dividing by (counter - 1) would fix it.