modifying libraries

i planning keypad library in sketch, i'm unshure if have asign pins in keypad.cpp file or in sketch. array keymapping:

// 4x4 keypad key mapping. shouldn't need touch unless have
// keypad different (or more) keys listed.
const char keymap[4][5] = {      "123a",
                       "456b",
                       "789c",
                       "*0#d"  };

if want make bigger matrix, how that? should change keymap array again in .cpp file , let ide recompile? should define matrix , array in sketch or should try make copy of lib , modify that?

al multidimensional arrays bit confusing. looking @  example above, result of

keymap[1][4]

or

keymap[4][1]

sorry question-mix

it may think of value in first bracket number of rows , second bracket value in each column.

keymap[1][4] 1  row of 4 characters (3 plus trailing 0 terminates string)
 or  
keymap[4][1] 4 rows of 1 character

so make keymap of 6 rows have:

keymap[6][5] = {"123a",
                         "456b",
                         "789c",
                         "*0#d",
                         "ghij",
                         "klmn"};

to make each of 4 rows of keymap have 7 characters  ( 6 characters plus terminating 0)

keymap[4][7] =  {"123abc",
                          "456bcd",
                          "789cde",
                          "*0#def"  };

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