Reject letter input without row number

[EricccTaiwan]

This patch improves input validation by ensuring that a letter input must be followed by a row number. If the user enters only a letter within the valid board range without a corresponding row number, an error message is displayed. This enhances clarity and prevents invalid moves, ensuring correct input handling.

Before

$ ./ttt
 1 |             
 2 |             
 3 |             
 4 |             
---+-------------
      A  B  C  D
X> 1
Invalid operation: No leading alphabet
X> 2
Invalid operation: No leading alphabet
X> a
X> b
X> c
X> d
X> e
Invalid operation: index exceeds board size
X> ^C
$

After

$ ./ttt
 1 |             
 2 |             
 3 |             
 4 |             
---+-------------
      A  B  C  D
X> 1
Invalid operation: No leading alphabet
X> 2
Invalid operation: No leading alphabet
X> a
Invalid operation: No row number
X> b
Invalid operation: No row number
X> c
Invalid operation: No row number
X> d
Invalid operation: No row number
X> e
Invalid operation: index exceeds board size
X> f
Invalid operation: index exceeds board size
X> ^C
$

[jserv]

Instead of "trailing number," use "row numbers" for precise naming.

[jserv]

The term "row numbers" is clearer and more standard, ensuring that the input includes both the row (number) and the column (alphabet).

[EricccTaiwan]

Thanks for your feedback! "row numbers" sounds clearer, but since only one row number is entered at a time, should it be singular ("row number") instead?

[jserv]

Thanks for your feedback! "row numbers" sounds clearer, but since only one row number is entered at a time, should it be singular ("row number") instead?

The term "row numbers" means the collection of the numbers in row, and you should use the form "row number" for each input.

[jserv]

Thank @EricccTaiwan for contributing!