Hello folks, I have a program that uses a linked list to implement a stack to convert a string from infix notation to postfix notation, and then to evaluate it. Well, the conversion part works just fine, but I have encountered a problem when trying to evaluate it. In my evaluate method, in the switch statement, when I try to compile, I get 4 errors (one for each case): possible loss of precision, found: int, required: char. I have everything set up as a char data type, no ints. I have no idea where it is getting these ints from. Any ideas, would be fantastic.
import javax.swing.JOptionPane;
public class InToPost {
private LinkList list;
private String inString;
private String outString = "";
public InToPost myStack;
public InToPost(String in) {
inString = in;
myStack = new InToPost();
}
public InToPost() {
list = new LinkList();
}
public void push(char j) {
list.insertFront(j);
}
public char pop() {
return list.deleteFront();
}
public boolean isEmpty() {
return (list.isEmpty());
}
public void displayStack() {
System.out.print("Stack: ");
list.displayList();
}
class LinkList {
private Link head;
public LinkList() {
head = null;
}
public boolean isEmpty() {
return (head == null);
}
public void insertFront(char d) {
Link newLink = new Link(d);
newLink.next = head;
head = newLink;
}
public char deleteFront() {
Link temp = head;
head = head.next;
return temp.data;
}
public void displayList() {
Link current = head;
while (current != null) {
current.displayLink();
current = current.next;
}
System.out.println("");
}
class Link {
public char data; // data item
public Link next; // next link in list
public Link(char d) {
data = d;
}
public void displayLink() {
System.out.print(data + " ");
}
}
}
public String doTrans() {
for (int j = 0; j < inString.length(); j++) {
char ch = inString.charAt(j);
switch (ch) {
case '+':
case '-':
gotOper(ch, 1);
break; // (precedence 1)
case '*': // it's * or /
case '/':
gotOper(ch, 2); // go pop operators
break; // (precedence 2)
case '(': // it's a left paren
myStack.push(ch); // push it
break;
case ')': // it's a right paren
gotParen(ch); // go pop operators
break;
default: // must be an operand
outString = outString + ch; // write it to output
System.out.println(outString);
break;
}
}
while (!myStack.isEmpty()) {
outString = outString + myStack.pop();
}
System.out.println(outString);
return outString; // return postfix
}
public void evaluate() {
char a;
char b;
for (int j = 0; j < outString.length(); j++) {
char result = 0;
char ch = outString.charAt(j);
switch (ch) {
case '+':
a = myStack.pop();
b = myStack.pop();
result = a + b;
myStack.push(result);
break;
case '-':
a = myStack.pop();
b = myStack.pop();
result = a - b;
myStack.push(result);
break;
case '*':
a = myStack.pop();
b = myStack.pop();
result = a * b;
myStack.push(result);
break;
case '/':
a = myStack.pop();
b = myStack.pop();
result = a / b;
myStack.push(result);
break;
default:
myStack.push(ch);
break;
}
}
System.out.println(myStack.pop());
}
public void gotOper(char opThis, int prec1) {
while (!myStack.isEmpty()) {
char opTop = myStack.pop();
if (opTop == '(') {
myStack.push(opTop);
break;
}// it's an operator
else {// precedence of new op
int prec2;
if (opTop == '+' || opTop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1) // if prec of new operator is less
{ // than prec of old
myStack.push(opTop); // save newly-popped operator
break;
} else
// prec of new operator is not less than prec of old
outString = outString + opTop;
}
}
myStack.push(opThis);
}
public void gotParen(char ch){
while (!myStack.isEmpty()) {
char chx = myStack.pop();
if (chx == '(')
break;
else
outString = outString + chx;
}
}
public static void main(String[] args) {
String inString = JOptionPane.showInputDialog("Enter your expression: ");
System.out.println(inString);
String outString;
InToPost theTrans = new InToPost(inString);
outString = theTrans.doTrans();
System.out.println("Postfix is " +outString+ '\n');
InToPost calculate = new InToPost(outString);
calculate.evaluate();
}
}Thank you,
jmasta