Plese Help, don't know what's wrong.

Question about the task

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It seems to be stuck in an endless loop, I don't know where is causing this problem. 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 .......

Initialize the MULTIPLICATION_TABLE array as a new int[10][10], fill it with a multiplication table, and then display it on the console in the following form: 1 2 3 4 … 2 4 6 8 … 3 6 9 12 … 4 8 12 16 … …

The numbers in each line are separated by a space.

Requirements:

In the main method, the MULTIPLICATION_TABLE array must be filled with a multiplication table.
The displayed text should contain 10 lines.
Each displayed line should contain 10 numbers separated by a space.
The displayed numbers must form a multiplication table.

package en.codegym.task.pro.task05.task0509; /* Multiplication table */ public class Solution { public static int[][] MULTIPLICATION_TABLE; public static void main(String[] args) { //write your code here MULTIPLICATION_TABLE=new int[10][10]; for(int i=0;i<10;i=i++){ for(int j=0;j<10;j++){ MULTIPLICATION_TABLE[i][j]=((i+1)*(j+1)); System.out.print(MULTIPLICATION_TABLE[i][j]+" "); } System.out.println(); } } }

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Samson-eth Java Developer

6 March 2023, 08:52

when you start the first loop it always starts from zero because you initialized it to be 0, in both cases int i = 0 and i = i++ // both are always zero for(i = 0; i < 10; i = i++) // this means you always set i to be zero(0), after each loop it starts i as 0 again and cant be reached to 10 not even 1; for(i = 0; i < 10; i++) //this will prevent from infinite loop and can be reached to 10 and terminate

Jill L

Level 10 , China, China

7 March 2023, 02:16

Why i=i++ is always 0 ?

Samson-eth Java Developer

7 March 2023, 07:02

since you assign "int i = 0" and you use post increment i++ then i = 0

Jill L

Level 10 , China, China

7 March 2023, 08:12

I still confused, what's the difference between i=i++ and i++? Since I think i=i++ logically equals i=i=i+1, first i=i+1, then i=i changes nothing.

Samson-eth Java Developer

7 March 2023, 09:33

ok try this instead of post increment use pre increment i = ++i Case 1 : i = i++ // i is always zero because you cant increment before i is executed and when you execute the next loop still i is 0 ... and continue like that Case 2: i = ++i // in this case you already assign the next value to i and next you assign the next ... and continue I hope now its clear

Jill L

Level 10 , China, China

8 March 2023, 02:19

Yes you are right. I thought i=i++ is equal to i=i=i+1, now I know this is wrong. i=i=i+1 is equal to i=i+1, but i=i++ is always 0, I know the difference between i++ and ++i, but I still don't understand why i=i++ isn't equal to i=i=i+1. anyway, thank you!

Thomas

Level 41 , Bayreuth, Germany

8 March 2023, 11:22

That's why, I commented the byte code. Also i = i + 1 is contradictory. The way it is treated by the compiler is the only logical way to get out of it. Java code:

int i = 0;
i = i++;

Decompiled bytecode:

0: iconst_0                  // load int 0 onto stack
1: istore_1                  // store stack value in local variable 1 (the past two commands mean: int i = 0)
2: iload_1                   // load value from variable 1 to stack (that's our i)
3: iinc          1, 1        // index, byte value -> increment local variable 1 by byte value 1, the local variable is now 1
7: istore_1                  // now save stack value back to local value, remember, stack holds 0 overwriting the 1

If you'd use a pre increment operator, then the stack would be saved back to the local variable before (pre) the iinc operation. And the incremented value would be the one you finally see in i. For the post increment the stack is saved back after (post) incrementing. That's why it assigns the original value. Btw. C/ C++ does it the same way.

Thomas

Level 41 , Bayreuth, Germany

25 February 2023, 15:08

i=i++ is the problem i will stay 0. I think Java does this a bit in a roundabout way. First it remembers the value to assign to i (because of the post increment), that's in the first iteration 0. Then it increments i and finally it assigns the memorized value (the zero) overwriting the incremented value again. Best is to use i++ or i += 1 or maybe i = i + 1. Even i = ++i should work. Just your approach unfortunately fails.

Jill L

Level 10 , China, China

26 February 2023, 01:15

Thanks! I originally wanted to use i++, but accidentally wrote i=i++，and I didn't realize it😅. Now I still a little confused about i=i++...