Strange error in sql*plus in a line with "&"

Question

Hi friends, this error is very strange:
Open your SQL*PLUS.
write this:
DECLARE
V_1 VARCHAR2(10);
V_2 VARCHAR2(10);
BEGIN
V_1:=&var1;
--V_2:=&var2;
END;
Why it ask me for a value to var2 ???????????
Does it ignore the -- at the begining of the line
(same result with /* */ )
Thanks,
Jose.

Answer 1

It is not an error.
There are two parsers here doing their thing. The SQL*Plus Parser. The Oracle (SQL and/or PL/SQL) parser.
SQL*Plus reads a line at a time and processs it. It has no idea whether or a line is actually a comment line for SQL or PL/SQL. It however does see that the line contains a SQL*PLUS substitution variable called &var2. Thus it prompts for a value for this variable (as VERIFY is ON). It substitutes &var2 with the value that the user supplies.
When the SQL*Plus parser encounters the end-of-block marker (the forward slash in this case), it transmits that block to the Oracle Server for execution. There the Oracle Server runs it through the PL/SQL or SQL parsers (depending on whether the block is SQL or anonymous PL/SQL).
Nothing strange about it. Nothing wrong with it.