Question

tack Assignment Objective: to be familiar with stack operations and applications Requirements: (a) Implement a Java program that take in an infix expression from the user and output the expression in postfix notation. (b) [15 points bonusl If all the operands in the input are numeric, then your program should evaluate the expression and display its value Hints: deta algorithm for converting an infix expression to the equivalent postf x listed at CSIS ace.edu/n wolf/CS122/infix ostfix.htm

Answer 1

Java Program :

import java.util.*;

public class PostfixConverter {
private String infixExpression;

public PostfixConverter(String infixExpression) {
this.infixExpression = infixExpression;
}

private String convertInfixExpression() {
StringTokenizer tokens = new StringTokenizer(infixExpression);
Stack operatorStack = new ArrayStack();
String converted = "";

while(tokens.hasMoreTokens()) {
String token = tokens.nextToken();
if(token.equals("(")) {
operatorStack.push(new String(token));
}
else if(token.equals(")")) {
while(operatorStack.top().equals("(") != true) {
converted = converted + " " + operatorStack.pop();
}
if(operatorStack.top().equals("(")) {
operatorStack.pop();
}
}
else if (isOperator(token)){
if(operatorStack.isEmpty() == true) {
operatorStack.push(new String(token));
}
else {
if(ICP(token) < ISP((String) operatorStack.top())) {
converted = converted + " " + operatorStack.pop();
operatorStack.push(token);
}
else {
operatorStack.push(new String(token));
}
}
}
else {
converted = converted + " " + new String(token);
}
}
while(operatorStack.isEmpty() != true) {
converted = converted + " " + operatorStack.pop();
}

return converted;
}

public int ISP(String token) {
int precedence = 0;
if(token.equals("+")|| token.equals("-")) {
precedence = 2;
}
else if(token.equals("*") || token.equals("/")) {
precedence = 4;
}
else if(token.equals("^")) {
precedence = 5;
}
else if(token.equals("(")) {
precedence = 0;
}
return precedence;
}

public int ICP(String token) {
int precedence = 0;
if(token.equals("+")|| token.equals("-")) {
precedence = 1;
}
else if(token.equals("*") || token.equals("/")) {
precedence = 3;
}
else if(token.equals("^")) {
precedence = 6;
}
return precedence;
}

private boolean isOperator(String token) {
return (token.equals("+") ||
token.equals("-") ||
token.equals("*") ||
token.equals("/") ||
token.equals("^") );
}

public static void main(String[] args) {
System.out.println("Input the infix expression "
+ "(operands, operators are separated by spaces):");
Scanner input = new Scanner(System.in);
String infixExpression = input.nextLine();
PostfixConverter converter = new PostfixConverter(infixExpression);
System.out.println("The converted expression is " +
converter.convertInfixExpression());
}

}