how to comparison operators in plsql

DECLARE
a number (2) := 21;
b number (2) := 10;
BEGIN
 IF (a = b) then
  dbms_output.put_line('Line 1 - a is equal to b');
  ELSE
  dbms_output.put_line('Line 1 - a is not equal to b');
 END IF;
 
 IF (a < b) then
  dbms_output.put_line('Line 2 - a is less than b');
  ELSE
  dbms_output.put_line('Line 2 - a is not less than b');
 END IF;

 IF ( a > b ) THEN
 dbms_output.put_line('Line 3 - a is greater than b');
 ELSE
 dbms_output.put_line('Line 3 - a is not greater than b');
 END IF;
 -- Lets change value of a and b
 a := 5;
 b := 20;

 IF ( a <= b ) THEN
  dbms_output.put_line('Line 4 - a is either equal or less than b');
 END IF;

    IF ( b >= a ) THEN
     dbms_output.put_line('Line 5 - b is either equal or greater than a');
      END IF;
 
     IF ( a <> b ) THEN
       dbms_output.put_line('Line 6 - a is not equal to b');
       ELSE
       dbms_output.put_line('Line 6 - a is equal to b');
     END IF;
 END;
/