-
Notifications
You must be signed in to change notification settings - Fork 0
/
PostfixEvaluation.java
75 lines (66 loc) · 2.39 KB
/
PostfixEvaluation.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
import java.util.Scanner;
public class PostfixEvaluation {
Stack2 stack2=new Stack2();
public int evaluatePostfix(String e){
for (int i=0;i<e.length();i++){
char c=e.charAt(i);
if (c==' ')
continue;
else if(Character.isDigit(c)) {
int n=0;
//extract the characters and store in n
while (Character.isDigit(c)){
n=n*10+ (int)(c-'0');
i++;
c=e.charAt(i);
}
//push the number into the stack
stack2.push(n);
}
//if the scanned character is an operator pop two elements from the stack and apply the operator
else {
int value1=stack2.pop();
int value2=stack2.pop();
switch (c){
case '+':
stack2.push(value2+value1);
break;
case '-':
stack2.push(value2-value1);
break;
case '/':
stack2.push(value2/value1);
break;
case '*':
stack2.push(value2*value1);
break;
}
}
}
return stack2.pop();
}
public static void main(String[] args){
PostfixEvaluation postfixEvaluation=new PostfixEvaluation();
//System.out.println(postfixEvaluation.evaluatePostfix(" 1 5 + 8 4 1 - - * "));
//System.out.println(postfixEvaluation.evaluatePostfix(" 2 3 4 + * "));
Scanner scanner = new Scanner(System.in);
int choice;
while(true){
System.out.println("Enter 1 to use the calculator and 0 to exit");
choice = scanner.nextInt();
scanner.nextLine();
if(choice==1){
System.out.println("Enter a postfix expression");
String expression = scanner.nextLine();
String expr = String.valueOf(expression).replaceAll(".", "$0 ");
System.out.println(postfixEvaluation.evaluatePostfix(expr));
}
else if (choice==0){
System.exit(0);
}
else {
System.out.println("Invalid input");
}
}
}
}