The postfix calculator redone using a switch statement.
import java.util.Stack;
import java.util.Scanner;
public class PostfixCalculatorSwitch {
/**
The program reads input of digits and symbols +,-,*,/ that
form a valid postfix expressions of binary arithmetic operations.
In postfix notation an operation follows its operands:
7 8 + means 7 + 8 and evaluates to 15.
2 3 + 7 * means (2 + 3) * 7 and evaluates to 35.
Postfix notation doesn't use parentheses.
In this program for simplicity we only use single digit numbers
as input and don't use spaces.
Example:
653*+83-+ = (6 + (5 * 3)) + (8 - 3) = 26
Minimum requirements:
The program doesn't handle spaces in data (it may give incorrect results)
If the input is not well-formed then an error may occur or an incorrect
result may be returned.
These requirements may be refined later
**/
public static void main(String [] args) {
// create a new scanner to read the data in
Scanner read = new Scanner(System.in);
// prompt the use for data
System.out.println("Please enter your input string");
// read the entire expression
String input = read.next(); // reads until a whitespace or new line
// print it back to make sure that it is read cotrrectly
System.out.println(input);
// create a new stack. It stores operands that still need
// to be evaluated
Stack<Integer> operations = new Stack<Integer>();
for (int i = 0; i < input.length(); ++i) {
// getting the next character of the string
char c = input.charAt(i);
// variables to store the operands are declared outside
// of if/else for easier reuse
int num1 = 0, num2 = 0;
// checking if the charcater is a digit
if (Character.isDigit(c)) {
operations.push(c - '0');
}
else {
switch(c) {
case '+':
num1 = operations.pop();
num2 = operations.pop();
operations.push(num2 + num1);
break;
case '-':
num1 = operations.pop();
num2 = operations.pop();
operations.push(num2 - num1);
break;
case '*':
num1 = operations.pop();
num2 = operations.pop();
operations.push(num2 * num1);
break;
case '/':
num1 = operations.pop();
num2 = operations.pop();
operations.push(num2 / num1);
break;
default:
System.out.println("Invalid operation: " + c);
}
}
}
// print the result
System.out.println(operations.pop());
}
}