DECLARE
	v_sal NUMBER (12) := '&Enter_salary';
	v_last_name VARCHAR2(10);
BEGIN
	SELECT last_name
	INTO v_last_name
	FROM my_emp
	WHERE salary=v_sal;
	DBMS_OUTPUT.PUT_LINE('Name: ' || v_last_name || ' Salary: ' || v_sal);
EXCEPTION
	WHEN TOO_MANY_ROWS THEN
	DBMS_OUTPUT.PUT_LINE('More than one employee with salary of ' || v_sal);
	WHEN NO_DATA_FOUND THEN
	DBMS_OUTPUT.PUT_LINE('No employees with salary of ' || v_sal);
	WHEN VALUE_ERROR THEN
	DBMS_OUTPUT.PUT_LINE('Not a number');	
	WHEN OTHERS THEN
	DBMS_OUTPUT.PUT_LINE('Some other error occured');
END;

Enter value for enter_salary: 1b
old   2:        v_sal NUMBER (12) := '&Enter_salary';
new   2:        v_sal NUMBER (12) := '1b';
DECLARE
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at line 2

v_sal NUMBER (12) := '&Enter_salary';

DECLARE
	v_sal NUMBER (12); 
	v_last_name VARCHAR2(10);
BEGIN
    v_sal := '&Enter_salary';
	
	SELECT ename
	INTO v_last_name
        ...

Enter value for enter_salary: 1b
old   5:     v_sal := '&Enter_salary';
new   5:     v_sal := '1b';
Not a number

PL/SQL procedure successfully completed.

SQL>