NOT on array Place

Question

I'm having this:

char board_game [3][3] = {0}; // The Board Game

And after this I'm doing that:

scanf("%d%d", &row, &col); // Get The Input And Put It In Row And Column
printf("%d",board_game[row][col]);

There is some output that I don't understand and what does that line mean board_game[row][col]?

|    input    | output
| row  | col  |
|______|______|________
|   0  |   0  |   0
|------|------|--------
|   0  |   1  |   0
|------|------|--------
|   0  |   2  |   0
|------|------|--------
|   0  |   3  |   0
|------|------|--------
|   1  |   0  |   0
|------|------|--------
|   1  |   1  |   0
|------|------|--------
|   1  |   2  |   0
|------|------|--------
|   1  |   3  |   0
|------|------|--------
|   2  |   0  |   0
|------|------|--------
|   2  |   1  |   0
|------|------|--------
|   2  |   2  |   0
|------|------|--------
|   2  |   3  |   1     **WHY 1?**
|------|------|--------
|   3  |   0  |   1     **WHY 1?**
|------|------|--------
|   3  |   1  |   0
|------|------|--------
|   3  |   2  |   0
|------|------|--------
|   3  |   3  |   0
|------|------|--------

Can you please explain to me what is going on?

The declaration `[3]` means that the indices 0 ... 2 are valid. 3 is not, therefore undefined behaviour. => if you needed index `3` to be valid, you must declare `char board_game[4][4] = {0}` — Antti Haapala -- Слава Україні, Oct 10 '17 at 11:57
If you don't understand what `board_game[row][col]` means, then perhaps you should [get a couple of good beginners books](http://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list) and start over by reading them? — Some programmer dude, Oct 10 '17 at 11:58
If you have [*undefined behavior*](https://en.wikipedia.org/wiki/Undefined_behavior) then *anything* could happen. In reality, what's happening is that you attempt to read memory that doesn't belong to you, and just read its contents. It might work, or it might crash. — Some programmer dude, Oct 10 '17 at 11:59
It's the value in that offsets, I know, but why it's 0 and 1 in Other Places — Programmmer_Z, Oct 10 '17 at 11:59
If you use a recent `gcc`, compile with `-fsanitize=undefined` and then run your program. — Antti Haapala -- Слава Україні, Oct 10 '17 at 11:59
Lastly, C doesn't have any kind of bounds checking. It's up to you to make sure the code doesn't go out of bounds. — Some programmer dude, Oct 10 '17 at 12:00
@Programmmer_Z it is 0 or 1 or anything, because the behaviour of your program is **undefined**. A butterfly flaps its wings - what will happen? — Antti Haapala -- Слава Україні, Oct 10 '17 at 12:00

score 0 · Answer 1 · answered Oct 10 '17 at 12:03

You are trying to access a memory location that doesnot belong to your array. When you define an array of size 3 the index are 0,1,2 . The values board game[0][3],board game[1][3],board game[2][3],board game[3][0],board game[3][1], board game[3][2],board game[3][3] are out of bound

Raz Luvaton · Accepted Answer · 2017-10-10T13:22:40.820

0

It's Out Of Bound and undefined (offsets: 3, 3| 3, 0) when the indexes only can be between 0..2

And you declared 0 at the start to all the array values

board_game[row][col] Means the value of the array in that offsets

edited Oct 10 '17 at 13:22

answered Oct 10 '17 at 12:05

Raz Luvaton

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NOT on array Place

2 Answers2