JavaScript

function Stack() {  this.dataStore = [];  this.top = 0;  this.push = push;  this.pop = pop;  this.peek = peek;  this.length = length;} function push(element) {  this.dataStore[this.top++] = element;} function pop() {  return this.dataStore[--this.top];} function peek() {  return this.dataStore[this.top-1];} function length() {  return this.top;} var infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3";infix = infix.replace(/\s+/g, ''); // remove spaces, so infix[i]!=" " var s = new Stack();var ops = "-+/*^";var precedence = {"^":4, "*":3, "/":3, "+":2, "-":2};var associativity = {"^":"Right", "*":"Left", "/":"Left", "+":"Left", "-":"Left"};var token;var postfix = "";var o1, o2; for (var i = 0; i < infix.length; i++) {  token = infix[i];  if (token > "0" && token < "9") { // if token is operand (here limited to 0 <= x <= 9)    postfix += token + " ";  }  else if (ops.indexOf(token) != -1) { // if token is an operator    o1 = token;    o2 = s.peek();    while (ops.indexOf(o2)!=-1 && ( // while operator token, o2, on top of the stack      // and o1 is left-associative and its precedence is less than or equal to that of o2      (associativity[o1] == "Left" && (precedence[o1] <= precedence[o2]) ) ||       // the algorithm on wikipedia says: or o1 precedence < o2 precedence, but I think it should be      // or o1 is right-associative and its precedence is less than that of o2      (associativity[o1] == "Right" && (precedence[o1] < precedence[o2]))       )){        postfix += o2 + " "; // add o2 to output queue        s.pop(); // pop o2 of the stack        o2 = s.peek(); // next round    }    s.push(o1); // push o1 onto the stack  }  else if (token == "(") { // if token is left parenthesis    s.push(token); // then push it onto the stack  }  else if (token == ")") { // if token is right parenthesis     while (s.peek() != "("){ // until token at top is (      postfix += s.pop() + " ";    }    s.pop(); // pop (, but not onto the output queue  }}while (s.length()>0){  postfix += s.pop() + " ";}print(postfix);