DECLARE
  V_Operator CHAR(1):= '&enterOpearator';
  V_Num1     NUMBER := &enterNum1;
  V_Num2     NUMBER := &enterNum2;
BEGIN
  IF V_Operator = '*' THEN
    DBMS_OUTPUT.PUT_LINE('Result of '||V_num1||' * '||V_Num2||' = '||(V_Num1*V_Num2));
  ELSIF V_Operator = '/' THEN
    DBMS_OUTPUT.PUT_LINE('Result of '||V_num1||' / '||V_Num2||' = '||(V_Num1/V_Num2));
  ELSIF V_Operator = '+' THEN
    DBMS_OUTPUT.PUT_LINE('Result of '||V_num1||' + '||V_Num2||' = '||(V_Num1+V_Num2));
  ELSIF V_Operator = '-' THEN
    DBMS_OUTPUT.PUT_LINE('Result of '||V_num1||' - '||V_Num2||' = '||(V_Num1-V_Num2));
  ELSE
    DBMS_OUTPUT.PUT_LINE('Invalid Operator');
  END IF;
END;
/

/*
  Program to swap 2 numbers if first one is greater than the second.
  Else print the two numbers as usual.
  Numbers are swapped without third variable.      
*/

DECLARE
  V_Num1 NUMBER :=&GNum1; --Local variable.
  V_Num2 NUMBER :=&GNum2; --Local variable.
BEGIN
  DBMS_OUTPUT.PUT_LINE('V_Num1 = '||V_Num1);
  DBMS_OUTPUT.PUT_LINE('V_Num2 = '||V_Num2);
  IF V_Num1 > V_Num2 THEN
    V_Num1 :=V_Num1+V_Num2;
    V_Num2 :=V_Num1-V_Num2;
    V_Num1 :=V_Num1-V_Num2;
    DBMS_OUTPUT.PUT_LINE('Swapped V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Swapped V_Num2 : '||V_Num2);
  ELSE
    DBMS_OUTPUT.PUT_LINE('Original V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Original V_Num2 ; '||V_Num2);
  END IF;
END;
/

/*
  Program to swap 2 numbers if first one is greater than the second.
  Else print the two numbers as usual.
*/

DECLARE
  V_Num1 NUMBER := &GNum1; --Local variable.
  V_Num2 NUMBER := &GNum2; --Local variable.
BEGIN
  DBMS_OUTPUT.PUT_LINE('V_Num1 = '||V_Num1);
  DBMS_OUTPUT.PUT_LINE('V_Num2 = '||V_Num2);
  IF V_Num1 > V_Num2 THEN
    V_Num1 :=V_Num1+V_Num2;
    V_Num2 :=V_Num1-V_Num2;
    V_Num1 :=V_Num1-V_Num2;
    DBMS_OUTPUT.PUT_LINE('Swapped V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Swapped V_Num2 : '||V_Num2);
  ELSE
    DBMS_OUTPUT.PUT_LINE('Original V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Original V_Num2 ; '||V_Num2);
  END IF;
END;
/

/*
  Program that takes two numbers and print their values.
  Swaps the number if first one is greater than the second one and print their swapped values.
  Else print their values as it is.
  Swapping is done by using a temporary variable.
*/

DECLARE
  V_Num1 NUMBER := &enterNum1; --First local variable.
  V_Num2 NUMBER := &enterNum2; --Second local variable.
  V_Temp NUMBER; --Temporary variable used for swapping.
BEGIN
  DBMS_OUTPUT.PUT_LINE('Inputted value of V_Num1 : '||V_Num1);
  DBMS_OUTPUT.PUT_LINE('Inputted value of V_Num2 : '||V_Num2);
  IF V_Num1 > V_Num2 THEN
    V_Temp :=V_Num1;
    V_Num1 :=V_Num2;
    V_Num2 :=V_temp;
    DBMS_OUTPUT.PUT_LINE('Swapped value of V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Swapped value of V_Num2 : '||V_Num2);
  ELSE
    DBMS_OUTPUT.PUT_LINE('Original value of V_Num1 : '||V_Num1);
    DBMS_OUTPUT.PUT_LINE('Original value of V_num2 : '||V_Num2);
  END IF;
END;
/

NULLs are very important consideration in any PL/SQL to make your program bug free. If you provide NULL values then always the ELSE part is executed.

/*
  The above program handling NULL values.
*/

DECLARE --First Block Begins.
  V_Num1 NUMBER := &enterNum1; --First local variable.
  V_Num2 NUMBER := &enterNum2; --Second local variable.
  V_Temp NUMBER; --Temporary variable used for swapping.
BEGIN
  DBMS_OUTPUT.PUT_LINE('Inputted value of V_Num1 : '||V_Num1);
  DBMS_OUTPUT.PUT_LINE('Inputted value of V_Num2 : '||V_Num2);
  IF V_Num1 IS NULL OR V_Num2 IS NULL THEN
    DBMS_OUTPUT.PUT_LINE('Fatal Error! Can''t Proceed. Enter valid numbers.');
  ELSE 
    IF V_Num1 > V_Num2 THEN
      V_Temp :=V_Num1;
      V_Num1 :=V_Num2;
      V_Num2 :=V_temp;
      DBMS_OUTPUT.PUT_LINE('Swapped value of V_Num1 : '||V_Num1);
      DBMS_OUTPUT.PUT_LINE('Swapped value of V_Num2 : '||V_Num2);
    ELSE
      DBMS_OUTPUT.PUT_LINE('Original value of V_Num1 : '||V_Num1);
      DBMS_OUTPUT.PUT_LINE('Original value of V_num2 : '||V_Num2);
    END IF;
  END IF;
END;
/

Q : Write a program to find whether a year is leap year or not?

Ans: Let us first understand what a leap year is.

A leap year occurs mostly every 4 years, but every 100 years we skip a leap year unless then number is divisible by 400.

• ✔ Leap years 1600, 2000
• ✘ Leap years 1700, 1800, 1900, 2100

/*
  Program to find if year entered is a leap year or not.
*/

DECLARE
  V_Year NUMBER(4) := &enterYear;
BEGIN
  IF V_Year <= 0 THEN
    DBMS_OUTPUT.PUT_LINE('Please enter a year greater than 0');
    EXIT;
  END IF;
  IF MOD(V_Year, 4) =0 THEN
    IF MOD(V_Year, 100) <>0 THEN
      DBMS_OUTPUT.PUT_LINE(V_Year||' is a Leap year.');
    ELSE
      IF MOD(V_Year, 400) =0 THEN
        DBMS_OUTPUT.PUT_LINE(V_Year||' is a Leap year.');
      ELSE
        DBMS_OUTPUT.PUT_LINE(V_Year||' isn''t a Leap year');
      END IF;
    END IF;
  ELSE
    DBMS_OUTPUT.PUT_LINE(V_Year||' isn''t a Leap year');
  END IF;
END;
/