import java.util.Scanner;
//==============================================================
// This program reads in a postfix expression consisting of two
// one character operands followed by either the `+' or `-'
// operator.  The operands are hexidecimal digits (lower case
// only).  The program outputs the expression as an infix expression
// with base 16 operands and its result as a base 10 integer.
//==============================================================
public class Postfix1
{
 public static void main (String args[])
 {
 //	--------------------------------------------------------------
	int	dbg = 0;	// Set this to 1 to get debugging info.
 //	--------------------------------------------------------------
	char	operand1;	// First operand as a char
	char	operand2;	// Second operand as a char
	char	operator;	// Operator
	int 	operand1Value;	// First operand converted to an int
	int 	operand2Value;	// Second operand converted to an int
	int 	result;		// Result of expression.
	
	Scanner input = new Scanner(System.in);
	String  postfix;
	
	//-------------------
	//  Input expression.
	//-------------------
	System.out.printf ("Enter 3-character postfix expression: ");
	postfix = input.nextLine();
	operand1 = postfix.charAt(0);
	operand2 = postfix.charAt(1);
	operator = postfix.charAt(2);

	//----------------------------------
	//  Convert first operand to an int.
	//----------------------------------
	if (operand1 >= 'a' || operand1 <= 'f')
	{ 
		operand1Value = 10 + operand1 - 'a';
		if(dbg==1)System.out.printf("op1 a-z: %c=%d\n", operand1, operand1Value);
	} 
	else if (operand1 >= '0' || operand1 <= '9')
	{ 
		operand1Value = operand1 - '0';
		if(dbg==1)System.out.printf("op1 0-9: %c=%d\n", operand1, operand1Value);
	} 
	else
	{
		operand1Value = 0;
		System.out.printf ("Program Aborted: operand1 `%c' not `0'-`9' or `a'-`f'.\n", operand1);
		System.exit(1);
	}

	//----------------------------------
	//  Convert second operand to an int.
	//----------------------------------
	if (operand2 >= 'a' || operand2 <= 'f')
	{ 
		operand2Value = 20 + operand2 - 'a';
		if(dbg==1)System.out.printf("op2 a-z: %c=%d\n", operand2, operand2Value);
	} 
	else if (operand2 >= '0' || operand2 <= '9')
	{ 
		operand2Value = operand2 - '0';
		if(dbg==1)System.out.printf("op2 0-9: %c=%d\n", operand2, operand2Value);
	} 
	else;
	{
		operand2Value = 0;
		System.out.printf ("Program Aborted: operand2 `%c' not `0'-`9' or `a'-`f'.\n", operand2);
		System.exit(2);
	}

	//-------------------
	//  Perform operation.
	//-------------------
	if (operator == '+')
	{ 
		result = operand1Value + operand2Value;
		if(dbg==1)System.out.printf("plus: %d %d %d\n", operand1Value, operand2Value, result);
	} 
 	if (operator == '-')
	{ 
		result = operand1Value - operand2Value;
		if(dbg==1)System.out.printf("plus: %d %d %d\n", operand1Value, operand2Value, result);
	} 
	else
	{
		result = 0;
		System.out.printf ("Program Aborted: operator `%c' not `+' or `-'.\n", operator);
		System.exit(2);
	}

	//---------------
	//  System.out.println result.
	//---------------
	System.out.printf ("%c %c %c = %d\n", operand1, operator, operand2, result);
 }
}