Question

Consider a system which has to accept prefix arithmetic expressions consisting of ‘+’(binary addition) , ‘-‘(binary subtraction), ‘*’(multiplication), ‘~’(unary subtraction), single digit numbers and compute their value.

Examples:

1. +12 → 3
2. ++12 → fail
3. +*123 → 5
4. *+123 → 9
5. +123 → fail

What parts would be required for such a system?

How do these parts relate to the concepts studied?

Could you write a program to implement such a system?

(Layout of the structure and the logic of the system, what are the components of such a system? Justification the possibility(or lack there of) of implementing such a system.)

Answer 1

Unary Operators:

The Unary Operators need a single operand. For instance, operations like incrementing/decrementing a value by one, negating an expression, or inverting the value of a Boolean.

Following are the Unary Operators supported in Java:

Operator	Description
+	Unary plus Operator; indicates a positive value
-	Unary minus Operator; negates an expression
++	Increment Operator; increments a value by 1
--	Decrement Operator; decrements a value by 1
!	Logical complement Operator; inverts the value of a Boolean

Java sample Program for Unary operations:

=====================================================

public class UnaryOperator

{

public static void main(String[] args) {

    int result_value = +10; // indicates positive value 10

    System.out.println(result_value);

    result_value --; // decrements the value of 10 by 1

    System.out.println(result_value);

    result_value ++; // increments the value of 9 by 1

    System.out.println(result_value);

    result_value = - result_value;// this minus operator negates an expression

    System.out.println(result_value);

    booleanisPass = false;

    System.out.println(isPass);

    System.out.println(!isPass);//o/p is inverted isPass value i.e. true

    }

}

Output:

Prefix and Postfix:

The increment/decrement operators are used before (prefix) or after (postfix) the operand. Even though, both the values will return the original value being incremented/decremented by one. The only difference is the prefix operator evaluates the operand to the incremented value, whereas the postfix version evaluates the operand to the original value.

Sample java program for prefix and postfix:

=======================================================

public class PreAndPost

{

        public static void main(String[] args)

{

        int a = 5;

            System.out.println(a++); // output is 5  

            System.out.println(a); // output is 6       

            System.out.println(++a); // output is 7

            System.out.println(a++); // output is 7

            System.out.println(a); // output is 8

        }

}

Output:

Operator	Name	Type
!	Logical NOT	Unary
&	Address-of	Unary
( )	Cast Operator	Unary
*	Pointer dereference	Unary
+	Unary Plus	Unary
++	Increment	Unary
–	Unary negation	Unary
––	Decrement 1	Unary
~	complement	Unary
,	Comma	Binary
!=	Inequality	Binary
%	Modulus	Binary
%=	Modulus assignment	Binary
&	Bitwise AND	Binary
&&	Logical AND	Binary
&=	Bitwise AND assignment	Binary
*	Multiplication	Binary
*=	Multiplication assignment	Binary
+	Addition	Binary
+=	Addition assignment	Binary
–	Subtraction	Binary
–=	Subtraction assignment	Binary
–>	Member selection	Binary
–>*	Pointer-to-member selection	Binary
/	Division	Binary
/=	Division assignment	Binary
<	Less than	Binary
<<	Left shift	Binary
<<=	Left shift assignment	Binary
<=	Less than or equal to	Binary
=	Assignment	Binary
==	Equality	Binary
>	Greater than	Binary
>=	Greater than or equal to	Binary
>>	Right shift	Binary
>>=	Right shift assignment	Binary
^	Exclusive OR	Binary
^=	Exclusive OR assignment	Binary
|	Bitwise inclusive OR	Binary
|=	Bitwise inclusive OR assignment	Binary
||	Logical OR	Binary