CODEWITHSUNDEEP
javarandom
Firefoxx Pwnass
Firefoxx Pwnass

Reputation: 135

I'm getting strange output from java program

I've some strange situation here and i thought that you may help me. I have an int array populated with numbers from 1 to 10. I want to generate random number from this array and save it to another int array. I used class Random to pick any number and since random throws 0 also i modify it like that ( so it throws numbers from 1 to 10 )

randNum = rand.nextInt(numbers.length-min+1)+min;

Following code makes sure that if it generates same random number, it skips it. Program is actually working and i'm getting in another array randomly positioned numbers from 1 to 10. That's what i wanted. But sometimes i'm missing one number from 1 - 10 AND iam Getting ZERO instead. Why?? 

int[] numbers = {1,2,3,4,5,6,7,8,9,10};
int[] usednum = new int[10];
Random rand = new Random();
int randNum;
int min = 1;

for (int x = 0; x<numbers.length; x++) {        
  for (int i = 0; i<usednum.length; i++) { 
    randNum = rand.nextInt(numbers.length-min+1) + min;
    for (int f = 0; f<usednum.length; f++) {
      if (usednum[f] == randNum) {
        break;
      } else if (usednum[f] == 0) { 
        usednum[x] = randNum;   
      }
    }
  } 
}

for (int c = 0; c<usednum.length; c++) {
  System.out.println(usednum[c]);
}

Upvotes: 0

Views: 416

Answers (7)

Mohayemin
Mohayemin

Reputation: 3870

Actually, you are never using the content of the array numbers. Try changing the array to something like int[] numbers = { 10, 22, 23, 42, 53, 18, 7, 8, 93, 10 };. You will get similar output.

Jon Lin's answer describe why your code is not working but does not address this issue. I think you will want to change your code to something like:

    int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    int[] usednum = new int[10];
    Random rand = new Random();

    int selectedCount = 0;

    while (selectedCount < numbers.length) {
        int randNum = numbers[rand.nextInt(numbers.length)];
        boolean contains = false;
        for (int x = 0; x < selectedCount; x++) {
            if (usednum[x] == randNum) {
                contains = true;
                break;
            }
        }

        if (!contains) {
            usednum[selectedCount] = randNum;
            selectedCount++;
        }
    }


    for (int c = 0; c < usednum.length; c++) {
        System.out.println(usednum[c]);
    }

Upvotes: 0

Duncan Jones
Duncan Jones

Reputation: 69339

If your goal is simply to shuffle an array of numbers, try this instead:

Integer[] numbers = {1,2,3,4,5,6,7,8,9,10};
Collections.shuffle(Arrays.asList(numbers));

It will have the same effect. Unless you are completing a homework assignment that forces you to solve the issue in a more manual fashion, just make use of the standard Java libraries.

The shuffle method writes changes through to the underlying Integer array, thanks to the special type of List returned by Arrays.asList(...). Note you have to use an array of Integer not int (see Why does Collections.shuffle() fail for my array?).

Upvotes: 2

Dan
Dan

Reputation: 1018

Edit - followed it and re-wrote it:

List<Integer> numbers = new LinkedList<Integer>(Arrays.asList(new Integer[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }));
        int[] usednum = new int[10];
        Random rand = new Random();
        int n = numbers.size();
        for (int i = 0; i < n; i++) {
            int randNum = rand.nextInt(numbers.size());
            usednum[i]=numbers.get(randNum);
            numbers.remove(randNum);
        }
        for (int c:usednum) {
            System.out.println(c); 
        }

Upvotes: 0

Miljen Mikic
Miljen Mikic

Reputation: 15241

Your array usednum is consisted of zeros at the beginning. In some cases, your program doesn't change that initial value, but breaks before at the line:

if(usednum[f] == randNum)

and does that during all iterations with same value x. X increments and there goes your chance to change the zero value.

Upvotes: 0

Minion91
Minion91

Reputation: 1929

you have one for loop too much.

remove the loop with the i iterator and the program should do what you want.

Oh and remove the -min+1 from the random generator, -1+1=0

Upvotes: 0

Jon Lin
Jon Lin

Reputation: 143876

You're inner-most for loop only checks if the current random number is in the usednum[] array. And the for loop immediately outer of that only checks 10 times total. It gives up too quickly because it only tries 10 random numbers. If all 10 are already used, nothing will get stored in that slot of usednum[] (thus it will be 0), try adding a while loop around that and get rid of the extraneous outer-most for loop:

        for(int i = 0; i<usednum.length; i++) {
           while(usednum[i]==0) {
              randNum = rand.nextInt(numbers.length-min+1)+min;
              for(int f = 0; f<usednum.length; f++) {
                 if(usednum[f] == randNum) {
                    break;
                 } //if                                                                                                                                        
                 else if (usednum[f] == 0) {
                    usednum[i] = randNum;
                 }
              }
           }
        }

Also note that the assignment is for usednum[i] = randNum;.

This is essentially replacing the middle for loop (the one that goes from i=0 to 9) with the while loop.

Upvotes: 2

Sign
Sign

Reputation: 1959

You are generating used numbers through an entire pass, so it doesn't generate a zero is just fails to generate a value it should.

Upvotes: 0

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