how to declare multiple variables in one line in oracle plsql block
No idea why you'd intentionally make your code less readable, but just... put them on one line:
set serveroutput onDECLARE A integer :=10;B integer :=5;BEGIN dbms_output.put_line(a ||':'|| b);END;/anonymous block completed10:5The semicolon is a statement separator within PL/SQL and it doesn't matter whether or not you have whitespace or new lines; unlike plain SQL run in SQL*Plus, say, where a new statement after a separator does have to be on a new line, but that's a client thing.
Maybe you mean something else though...