1. Construct a new method named 'evaluate' in the program to evaluate the result of the postfix string expression that is generated after converting from its infix form.

2. Add the code to call the method in main method, and also output the result to the output file 'out2a.txt'.

See the sample output below to get an idea. Postfix of the string is what, needed to be evaluated

I am providing the code that I have below, just need to add a method to evaluate the postfix expression.

Step3.java:

import java.io.BufferedWriter; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStreamWriter; import java.io.UnsupportedEncodingException; import java.io.Writer;

public class Step3 { // Expression string static String expression = "9.5 - 4 * 3 ^ 2 / 6 + 8 * 4"; public static void main(String[] args) { // Create SymbolTable object SymbolTable st = new SymbolTable(expression); // Printing the required information in Console // Display my Name System.out.println(""); // Display expression System.out.println("Valid Expression: " + expression); // Display operator String System.out.println("Operator String: " + st.strOperator); System.out.println(); // Display symbol table System.out.println("Symbol Table: "); System.out.println(st); // Variable String System.out.println("Variable String: " + st.strVariable); // Display infix System.out.println("Infix of the expression: " + st.buildInfix()); // Display the postfix Step3 obj = new Step3(); System.out.println("Postfix of the expression: " + obj.infix2Postfix(expression) );

// Printing the required information in Output File try (Writer writer = new BufferedWriter(new OutputStreamWriter( new FileOutputStream("C:/Users/patel/Desktop/JavaFiles/out2a.txt")))) { // Display my Name writer.write(""); ((BufferedWriter) writer).newLine(); // Display the expression writer.write(" Valid Expression: " + expression); ((BufferedWriter) writer).newLine(); // Display the operators only writer.write("Operator String: " + st.strOperator); ((BufferedWriter) writer).newLine(); ((BufferedWriter) writer).newLine(); // Display the symbol table writer.write("Symbol Table: "); ((BufferedWriter) writer).newLine(); // GETTING ERRORS HERE //int size = st.size(); //for (int i = 0; i < size; i++) //{ //writer.write(st.table); //((BufferedWriter) writer).newLine(); //}

// Display the operands used writer.write("Variable String: " + st.strVariable); ((BufferedWriter) writer).newLine(); // Display the infix of expression writer.write("Infix of the expression: " + st.buildInfix()); ((BufferedWriter) writer).newLine(); // Display the postfix of expression writer.write("Postfix of the expression: " + obj.infix2Postfix(expression)); } catch (UnsupportedEncodingException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } private boolean isOperator(char c){ if(c == '+' || c == '-' || c == '*' || c =='/' || c == '^') return true; return false; } /** * Checks if c2 has same or higher precedence than c1 * @param c1 first operator * @param c2 second operator * @return true if c2 has same or higher precedence */ private boolean checkPrecedence(char c1, char c2) { if((c2 == '+' || c2 == '-') && (c1 == '+' || c1 == '-')) return true; else if((c2 == '*' || c2 == '/') && (c1 == '+' || c1 == '-' || c1 == '*' || c1 == '/')) return true; else if((c2 == '^') && (c1 == '+' || c1 == '-' || c1 == '*' || c1 == '/')) return true; else return false; } /** * infix2Postfixs infix expression to postfix * @param infix infix expression to be infix2Postfixed * @return postfix expression */ public String infix2Postfix(String infix) { String postfix = ""; //equivalent postfix is empty initially Stack s = new Stack(100); //stack to hold symbols s.push('#'); //symbol to denote end of stack for(int i = 0; i < infix.length(); i++) { char inputSymbol = infix.charAt(i); //symbol to be processed if(isOperator(inputSymbol)) { //if a operator //repeatedly pops if stack top has same or higher precedence while(checkPrecedence(inputSymbol, s.peek())) postfix += s.pop(); s.push(inputSymbol); } else if(inputSymbol == '(') s.push(inputSymbol); //push if left parenthesis else if(inputSymbol == ')'){ //repeatedly pops if right parenthesis until left parenthesis is found while(s.peek() != '(') postfix += s.pop(); s.pop(); } else postfix += inputSymbol; } //pops all elements of stack left while(s.peek() != '#') { postfix += s.pop(); } return postfix; } public static int evaluate(String postfix) { // Add required code here (make new methods if required, to evaluate the expression) } }

Sample Output:

Valid Expression: 9.5 - 4 * 3 ^ 2 / 6 + 8 * 4 Operator String: -*^/+*

Symbol Table: A 9.5 B 4.0 C 3.0 D 2.0 E 6.0 F 8.0 G 4.0

Variable String: ABCDEFG Infix of the expression: A-B*C^D/E+F*G Postfix of the expression: 9.5 4 3 2 ^* 6 /- 8 4*+