Java: Multi Dimensional array output confusion?

Question

public class VarNoOfCols {
    public static void main(String[] args) {
        int a[][] = new int[3][];

        a[0]=new int[3];
        a[1]=new int[2];
        a[2]=new int[1];
        int temp=3;
        for(int i =0; i<3;i++) {
            for(int k=0;k<temp;k++) {
                a[i][k]= k*10;
                           temp-- ;
            }


        }
    }
}

--- output that I assumed ---- is below ---But this is incorrect.

(0 0) 0  (0 1) 10
(1 0) 0  (1 1) 10
(2 0) 0  (2,1) 10

I know this is incorrect. (My question is - on completing second iteration, "k" is greater than "temp" and when conditon fails it will stop the inner statments and do the next job (what ever it suppose to be).Why am i getting (0,2) = 20 and why i dont see (2,1) = 10 ?

You can see the correct output:

(0 0) 0  (0 1) 10 (0 2) 20
(1 0) 0  (1 1) 10
(2 0) 0

I am a learner and i really appreciate someone's help here. thank you

The programm you gave return the 2nd output (the one you said is correct) so I don't understand your question, and what is the first output you told about? Do you want to know why your app is giving you the 2nd output? — alain.janinm
– alain.janinm, Commented May 5, 2012 at 10:45
To alain - Yes, I am getting 2nd output. I have no clue why I am getting the 2nd output as specified. I am expecting the first output that I have mentioned. can anyone explain please? — MKod
– MKod, Commented May 6, 2012 at 7:06
@MKod You can't obtain the first output see my answer to know why. — alain.janinm
– alain.janinm, Commented May 6, 2012 at 8:58

Boris Strandjev · Accepted Answer · 2012-05-05 10:35:20Z

1

Change the code like that:

for(int i =0; i<3;i++)
{
    for(int k=0;k<3;k++)
        a[i][k]= k*10;

}

If you wanted a square output, why do you use the control variable temp that will change the number of outputted entries on each iteration over i?

answered May 5, 2012 at 10:35

Boris Strandjev

47.1k16 gold badges112 silver badges136 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Mayank K. Swami · Accepted Answer · 2012-05-06 07:44:48Z

0

this is because the temp and the k

in your program first i=0

k=0,temp=3 then (0 0) so output 0*10 = 0
k=1,temp=2 then (0 1) so output 1*10 = 10
k=2,temp=1 condition false in for loop (there the condition in the outer for loop(having i) is correct but in the inner for loop the condation k

i=1

k=0,temp=3 then (1 0) so output 0*10 = 0
k=1,temp=2 then (1 1) so output 1*10 = 10

i=2

k=0,temp=3 then (2 0) so output 0*10 = 0
k=1,temp=2 then (2 1) so output 1*10 = 10

there is no need of temp. to get correct output use this

for(int i =0; i<3;i++)
{
   for(int k=0;k<3;k++)
      a[i][k]= k*10;

}

edited May 6, 2012 at 7:44

answered May 5, 2012 at 10:36

Mayank K. Swami

57.3k23 gold badges130 silver badges148 bronze badges

1 Comment

MKod Over a year ago

The temp variable should be inside the (inner) 2nd loop. I am sorry initially I have given temp variable outside inner loop (2nd) .I am getting the 2nd output and not the first one as you and me (Mayank) expected. Can you please explain? Thank You

alain.janinm · Accepted Answer · 2012-05-06 08:57:46Z

0

Actually with your last edit (with temp-- in the second for) you obtain neither the first nor the second output.

Why?

Because you never reassign temp and after 3 time be decremented the second loop will not be executed anymore. So you got a value for (0;0) (0;1) and (1;0) only.

Why you can't obtain output 1 (square one)?

a[2] have a size of 1 so you can't have something in (2;1)

How to obtain the second output?

Don't put the temp-- in the second loop but after the second loop (at the end of the first loop).

answered May 6, 2012 at 8:57

alain.janinm

20.1k11 gold badges67 silver badges114 bronze badges

Comments

bluish · Accepted Answer · 2012-05-07 11:46:08Z

0

public class VarNoOfCols {           
    public static void main(String[] args) { 

        int a[][] = new int[3][];

        a[0]=new int[3];
        a[1]=new int[2];
        a[2]=new int[1];

        int temp=3;

        for(int i =0; i<3;i++)
        {
            for(int k=0;k<temp;k++)
                //the inner for lopp doesn't have curly "{" braces.
                //temp will be 3 for 1st loop and when k becomes 3 it exit inner loop.
                a[i][k]= k*10;
            temp--;
        }
        //temp--;
        //System.out.println("temp : " +temp + " \n " );

    }   
}

Thank you guys. I figuered out the logic behind. it is not logic, it is just that { that should be watched. I will get following output if I don't use braces { in inner loop:

(0 0 ) 0   (0 1 ) 10   (0 2 ) 20
(1 0 ) 0   (1 1 ) 10
(2 0 ) 0

If the braces { and } present in inner loop with temp variable inside inner loop then I will get the following output:

(0 0 ) 0   (0 1 ) 10
(1 0 ) 0

edited May 7, 2012 at 11:46

bluish

27.5k28 gold badges126 silver badges185 bronze badges

answered May 6, 2012 at 10:34

MKod

8235 gold badges20 silver badges34 bronze badges

1 Comment

alain.janinm Over a year ago

It's logic...If you don't put {} after the for loop only the first following statement is considered to be in the for-loop.

Collectives™ on Stack Overflow

Java: Multi Dimensional array output confusion?

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related