How to define 2D array in C

Question

I have to make a 2D array that carries the information of a table

I can't find the syntax error in the following

int majorPositions[][]={{0,90,-90},{90,15,90},{-45,-30,30},{0,60,0}};

also, how do I enter last column details as it is a char, not an integer

If you're going to stick with integers, encode the on/off as 1/0. Alternatively, create a structure type with elements x, y, z and tool — which need not all be integers. This would have an additional advantage; you'd only need a 1D array (of structures), not a 2D array (of integers). — Jonathan Leffler
– Jonathan Leffler, Commented Jun 12, 2019 at 4:26

gxexx · Accepted Answer · 2019-06-12 04:24:36Z

2

You have to set the size of the array like so:

int majorPositions[][3]={{0,90,-90},{90,15,90},{-45,-30,30},{0,60,0}};

or

int majorPositions[4][3]={{0,90,-90},{90,15,90},{-45,-30,30},{0,60,0}};

If your last column is just ON/OFF, cant you just represent it as a 1 or 0?

answered Jun 12, 2019 at 4:24

gxexx

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3 Comments

Gurjot kaur Over a year ago

no i cant replace it. coz 0 and 1 are TRUE and FALSE in my code

Gurjot kaur Over a year ago

Sorry, my bad...0 is False and 1 is True. i just mistyped it

gxexx Over a year ago

Like Jonathan said, a structure would be a good choice. You will be able to name the struct variables X,Y,Z,Tool to make it easier for others to understand your code.

Masahiro Wada · Accepted Answer · 2019-06-12 04:24:55Z

1

You have to specify the size of inner array as following.

int majorPositions[][3]={{0,90,-90},{90,15,90},{-45,-30,30},{0,60,0}};

And, I think you can encode ON and OFF into 1 and 0.

answered Jun 12, 2019 at 4:24

Masahiro Wada

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7 Comments

Gurjot kaur Over a year ago

0 and 1 are FALSE and TRUE in my code...being used for something else. any other suggestion?

Jonathan Leffler Over a year ago

@Gurjotkaur: Since ON and OFF are separate from TRUE and FALSE, there's no problem using 1 and 0 for ON and OFF, as well as using 1 for TRUE and 0 for FALSE (but 0 for TRUE and 1 for FALSE is completely anti-idiomatic C). You could use enum ToolAttached { OFF = 0, ON = 1 } and then enum ToolAttached tool; as part of a structure.

Gurjot kaur Over a year ago

@JonathanLeffler after defining ON AND OFF as 1 and 0. the code: int majorPositions[4][4]={{0,90,-90,OFF},{90,15,90,ON},{-45,-30,30,ON},{0,60,0,OFF}}; is also syntax error

kiran Biradar Over a year ago

@Gurjotkaur There should be some info displayed along with that error.

Ajay Brahmakshatriya Over a year ago

@Gurjotkaur you can use 1/0 for ON/OFF AND TRUE/FALSE. There is no issue with that. The context in which the values are used determines whether it is representing TRUE/FALSE or ON/OFF.

|

user694733 · Accepted Answer · 2019-06-12 07:40:37Z

1

I would use something like (like the other mention above)

#include <stdbool.h>

typedef struct
{
   int x;
   int y;
   int z;
   bool Tool;
} TableEntry_t;

TableEntry_t majorPositions[4];

It´s a clear solution and you can easily extend the table if you want.

edited Jun 12, 2019 at 7:40

user694733

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answered Jun 12, 2019 at 5:26

Kampi

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4 Comments

the busybee Over a year ago

If you #include <stdbool.h> you could use bool as a type and true and false as values. I'd never define booleans myself. This header was introduced 20 years ago in C99.

Lundin Over a year ago

Using a struct will probably lead to less efficient code though. The compiler is going to pad that bool to alignment anyway.

Kampi Over a year ago

You can avoid this when you add __attribute__ ((packed)). In this case the compiler don´t pad (if the compiler uses a padding). If the compiler doesn´t pad you don´t need this.

Jonathan Leffler Over a year ago

The compiler doesn't pad for fun; it does so because the code will be more efficient than if it is unpadded.

Lundin · Accepted Answer · 2019-06-12 08:33:42Z

0

You need to type out the inner dimension size(s) explicitly. To simplify everything, consider taking advantage of the fact that booleans in C are just glorified integers. You can use an int as bool and vice versa.

#include <stdbool.h>

int majorPositions[][4]=
{
  {  0,  90, -90, false },
  { 90,  15,  90, true  },
  {-45, -30,  30, true  },
  {  0,  60,   0, false },
};

You can get the size of this array at compile-time using sizeof(majorPositions)/sizeof(majorPositions[0]) (which will be 4 in this case).

Alternatively use a struct as proposed in other answers. It may or may not give less efficient code.

answered Jun 12, 2019 at 8:33

Lundin

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Comments

laddu · Accepted Answer · 2019-06-12 09:29:29Z

0

In two dimensional arrays, you must specify second dimension of an array during the declaration.

int majorPositions[][3]={{0,90,-90},{90,15,90},{-45,-30,30},{0,60,0}};

answered Jun 12, 2019 at 9:29

laddu

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