How to combine array?

Projects Programming
1

Hi,
May I use:

int dataNumber = 0; 
char msgA[asdf];
char msg[];

void setup()
{
}

void loop()
{
char msg[] = "msgA" + "dataNumber" ;
}

Thanks
Adam

2

The great thing about Arduino is that in the time it took you to post this, you could have tried it.

(No)

1 Like
3

No chance this ever compiles... what is `asdf``? how many bytes do you want in the msg array?

you might want to have a look at the String class (but it comes with "strings attached")

2 Likes
4

What is it that you want to accomplish?

Not how to declare an array. Inside the square bracket goes the size or the index of an element of the array. A string is a special kind of an array and is declared differently.

You cannot build an array like that. You could, like @J-M-L says, use Strings, but those can be risky to use. Simple strings are safer at first. Use sprintf (or snprintf) or strcpy and strcat to build the array.

2 ways to build the array.

int dataNumber = 0;  // ********** what is this for? ***********
char msgA[] = "asdf";  // a string declared
char msgB[] = "datanumber";  // a string declared
char msg[16];  // MUST be big enough to hold both arrays and the terminator (\0)

void setup()
{
   Serial.begin(9600);
   // use sprintf to build a string
   sprintf(msg, "%s%s", msgA, msgB);
   Serial.print("msg after sprintf < ");
   Serial.println(msg);
   // use copy and concatenate to build the string
   msg[0] = '\0'; // empty the string
   strcpy(msg, msgA);
   strcat(msg, msgB);
   Serial.print("msg after copy, concatenate < ");
   Serial.println(msg);
}

void loop()
{
}
1 Like
5

looks like you may be confusing access to a variable by using a string: "dataNumber" vs a symbol: dataNumber

1 Like
6

Thanks.
actually I just like to have : char combined with a string.

7

I really wish I knew what that meant

1 Like
8

Is that right, OP?

Then like so?

   sprintf(msg, "%s%d", msgA, dataNumber);
   Serial.print("msg after sprintf < ");
   Serial.println(msg);

If not, kindly explain. Give an example of the output.

1 Like
9

FYI:
char msg[] = "msgA" + "dataNumber" ;
is not valid.

char msg[] = "msgA" "dataNumber" ;
is valid and equivalent to:
char msg[] = "msgAdataNumber" ;
(Adjacent string constants are merged.)

If you wanted 'msgA' to be a variable, you can do something similar with preprocessor macros:

#define msgA "asdf"
char msg[] = msgA "dataNumber" ;

After macro expansion, the second line becomes:
char msg[] = "asdf" "dataNumber" ;
which is equivalent to:
char msg[] = "asdfdataNumber" ;

1 Like
10

Thanks.
I have:

char msgQ[] = "Stationcommand"; 
String a= A1;
I like to have:
char msg[] = "StationcommandA1";

How to get it please.

11

Great!
Thanks you.
The dataNumber is variable and may be = abc or CDE

char msgQ[] = "Stationcommand"; 
String a= ASD;

I like to have:
char msg[] = "StationcommandASD";

Thanks

12

On say, a Uno, A1 has the value 15
I'm not sure you can assign that directly to a String

(Never tried)

1 Like
14

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