char array variable name want to use in variable in Arduino IDE - arduino

Question

i created char array
char Jan1[] = "1,2,3,4";
char Jan2[] = "5,7,3,4";
char Jan3[] = "10,9,3,4";`
the above char arrays i want to use it as shown below in for loop each time it will iterate and print, print is an example i am processing this string further in code, but it is giving error. if instead of yy i use Jan1 then it is printing properly. what is the other way i can use yy as to get print char array as string.
for(int i=1;i<=2;i++)
{
char yy[4];
sprintf(yy,"Jan%d",i);
String presentMonth = String(yy);
Serial.print(presntMonth);
}

Answer 1

So by the comments it seems that what you want is to print the contents of the JanX variable based on an index variable.
Missunderstanding
First of all you need to understand the difference between strings as datatypes and variable names. The former are ways to represent a sequence of characters (used mainly, but not only, to display output messages to any sort of output like a file, a console etc..). The latter are names that you use while coding and they can be whatever you want but they will never appear in the final program.
This for instance creates a String (datatype) named hello which contains the sequence of characters h e l l o.
String hello = "Hello";
Nothing prevents me to assign goodbye to it:
hello = "Goodbye"
Serial.print(hello); // This will print "Goodbye"
In general (apart from very hacky ways) you can't retrieve the name of the variable from your program and have them ready in your executable.
Issue
char Jan1[] = {'1','2','3'};
String yy = "Jan1"
Serial.print(yy); // This will print "Jan1"
To print the items in Jan1 you need to iterate through the values.
void printItems(char* s,int N){
for ( i = 0; i<N; i++ )
{ Serial.print(s[i]); }
}
Since Arduino provides the String class, however, it would be better to do this:
String Jan1 = "1,2,3,4";
Serial.print(Jan1); // This iterates under the hood, takes care of the length, and all the good stuff.
Solution
You want to do something a little more advanced, you want to point to a particular string based on a variable, then print the content of the retrieved string.
I can think of two ways for doing so: by using an list of strings or via a hashmap.
List of strings
String list[] = {"1,2,3,4" , "4,5,6,7", ... };
for(int i = 0; i < sizeof(list)/sizeof(String) ; i++ ){
Serial.print(list[i])
}
Hashmap
The reason I am thinking about this is because you want a string as the "index" that let's you lookup the string, so you can "search" by name. The easiest and quickest method I can think of is to declare an array of structs string_name;string_content and use strcmp to iterate through the array of structs until the needed one is found.
typedef struct{ String name; String content;} element_t;
element_t dict[] = { {"Jan1","1,2,3,4"} , {"Jan2","2,3,4,5"} ... }'
// Note this is not even close to perfect (for instance lacks check if key does not exists)
String lookup(element_t DICT, int DICT_SIZE, String key){
// Iterate through the elements, use strcmp to retrieve it
for(int i = 0; i < DICT_SIZE ; i++ ){
if(strcmp(DICT[i].name,key) {
return DICT[i].content;
}
}
}
// Now create the key, as in your code, and then lookup.
for(int i=1;i<=2;i++)
{
char yy[4];
sprintf(yy,"Jan%d",i);
String presentMonth = lookup(dict,dict_size,yy);
Serial.print(presntMonth);
}