Using an array in a do....while statement

Question

I am trying to use a do...while loop that loops based on the id's in my array. I am a little new to using the do while loop, so am having some trouble incorporating the array into the thing. Here is my relevant code:

    String studentId   = StringUtils.defaultString(request.getParameter("Student_ID"));
    String studentId1  = StringUtils.defaultString(request.getParameter("Student_ID1"));   
    String studentId2  = StringUtils.defaultString(request.getParameter("Student_ID2"));
    String studentId3  = StringUtils.defaultString(request.getParameter("Student_ID3"));
    String studentId4  = StringUtils.defaultString(request.getParameter("Student_ID4"));
    String studentId5  = StringUtils.defaultString(request.getParameter("Student_ID5"));
    String studentId6  = StringUtils.defaultString(request.getParameter("Student_ID6"));
    String studentId7  = StringUtils.defaultString(request.getParameter("Student_ID7"));
    String studentId8  = StringUtils.defaultString(request.getParameter("Student_ID8"));
    String studentId9  = StringUtils.defaultString(request.getParameter("Student_ID9"));


    String[] studentArray;
    studentArray = new String [15];
        studentArray[0]  = studentId;          studentArray[1]  = studentId1;
        studentArray[2]  = studentId2;         studentArray[3]  = studentId3;
        studentArray[4]  = studentId4;         studentArray[5]  = studentId5;
        studentArray[6]  = studentId6;         studentArray[7]  = studentId7;
        studentArray[8]  = studentId8;         studentArray[9]  = studentId9;


do {
    // blah blah blah
} while (  // Here is where I want to tell it to loop for every student in my array.  It should not run for id's that are empty strings(*if possible));

See comments for a more clear explanation. The StringUtils.defaultString that is used when i am getting my parameters will give me an empty string if the param receives a NULL. So if possible I would like to take that into account, and not run my "do {}" statements when the particular array ID is an empty string. Thanks in advance for the help, and if you have any questions, please ask.

Why specifically a do...while loop? This could easily be done with a foreach loop — fge
– fge, Commented Jan 3, 2012 at 21:44
@fge yes, I believe that a for each loop would work as well, I was just curious how a do while might work, but using an array in for each loop is still a problem for me. — Mr Man
– Mr Man, Commented Jan 3, 2012 at 21:46
studentArray.length will tell you how many elements are in the array. It's easier to iterate over the array with for (int i = 0; i < studentArray.length; i++), but you can simulate that with do/while if you keep and "manually" increment/test your own index variable. — Hot Licks
– Hot Licks, Commented Jan 3, 2012 at 21:47
@HotLicks thank you for the tips, it makes since to do a for loop now that i see it written out, Idk why the array was tripping me up so much — Mr Man
– Mr Man, Commented Jan 3, 2012 at 21:49

MAK · Accepted Answer · 2012-01-03 21:59:50Z

5

This is better done using a for each loop:

for(String x:studentArray){
  // do what you want to do with x
}

To skip over values that are null, just insert an if check at the beginning of the loop and continue if x is empty.

edited Jan 3, 2012 at 21:59

answered Jan 3, 2012 at 21:45

MAK

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1 Comment

Aravind Yarram Over a year ago

@mak - 'x' can never be null as the OP is pre-processing it already

Aravind Yarram · Accepted Answer · 2012-01-03 21:46:43Z

4

Using enhanced for loop is simple

for(String student: studentArray)
{
  if(!student.equals(""))
  {
    //process data
  }
}

NOTE: The if condition can also be written as !"".equals(student) but it is not necessary in your scenario as you are already making sure the id's are never null by using StringUtils.defaultString

answered Jan 3, 2012 at 21:46

Aravind Yarram

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Comments

Makoto · Accepted Answer · 2012-01-03 21:47:31Z

4

The only difference between a do...while loop and a while loop is that the former is always executed at least once.

With that in mind, we can write code as if we were writing a standard while loop, keeping in the back of our minds that this loop will run through at least once.

int i = 0; // Some counter to keep track of the index position
do {
    if(!(studentArray[i] == null || studentArray[i] == "")) {
        // Good stuff here
    }
    i++;
} while(i < studentArray.length);

answered Jan 3, 2012 at 21:47

Makoto

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2 Comments

Hot Licks Over a year ago

You forgot to check if the array is empty.

Makoto Over a year ago

If one initializes the array, at worst its base value will be "". If one assigns values into the array, at worst its base value will be null, 0, or false. I work form the assumption (and intent of the original code) that the array is not empty, but you are otherwise absolutely right.

Hot Licks · Accepted Answer · 2012-01-03 21:51:05Z

1

int i = 0;
if (studentArray.length > 0) {
    do {
        doSomethingWithArrayElement(studentArray[i]);
        i++;
    } while (i < studentArray.length);
}

answered Jan 3, 2012 at 21:51

Hot Licks

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Comments

Brandon Poole · Accepted Answer · 2012-01-03 21:53:25Z

        string[] arr = new string[4]; // Initialize
        arr[0] = "one";               // Element 1
        arr[1] = "two";               // Element 2
        arr[2] = "three";             // Element 3
        arr[3] = "four";              // Element 4

        // Loop over strings
        foreach (string s in arr)
        {
            if (!String.IsNullOrEmpty(s))
            {
                Console.WriteLine(s);
            }
        }

        // do while
        var aValue = "Not Empty";
        do
        {
            //loop through elements here
            for (int a = 0; a < arr.Length; a++)
            {
                aValue = arr[a];
            }

        } while (!String.IsNullOrEmpty(aValue));

C# may be like Java, but it isn't exactly Java. It also seems that you've missed the point of the do...while; it seems that, if the last element is empty in the array, it will terminate, but not a step before.

Joshua Nyarko Boateng · Accepted Answer · 2020-10-27 16:08:14Z

This a sample code using arrays This Program Uses Do.... While Loop to Loop over a whole program when there is a user prompt.

package doWhileLoop;

import java.util.Scanner;

public class doWhileLoop {
    public static void main(String[] args) {
        //this is a program to prompt a user to continue or pass using the do while loop
        String programCounter;
        do {
            int sum=0;
            int list[] = new int[3];
            Scanner in = new Scanner(System.in);
            System.out.println("Enter  3 numbers to be added: ");
            for (int i = 0; i < 3; i++) {
                list[i] = in.nextInt();
                sum+= list[i];
            }
            System.out.println("sum = "+ sum);

            System.out.println("Enter Yes to continue or No to exit........");
            programCounter = in.next();

        }
        while (programCounter.equals("yes"));

    }
}

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