1. The following function converts a postfix expression to an infix expression assuming the expression can only contain unsigned integer numbers and + and - operators.

2. 1. public static String convert(String postfix) {

   2. String operand1, operand2, infix;

   3. Stack s = new AStack;

   4. int i = 0;

   5. while(i < postfix.length) {

   6. char nextc = postfix.charAt(i);

   7. if ((nextc == '+')||(nextc == '-') {

   8. operand2 = s.pop(); operand1 = s.pop();

   9. infix = '(' + operand1 + nextc + operand2 + ')';

   10. s.push(infix); i++;

   11. }

   12. else if (Character.isDigit(nextc)){

   13. int start = i;

   14. while(Character.isDigit(postfix.charAt(i)) i++;

   15. infix = postfix.substring(start,i);

   16. s.push(infix);

   17. }

   18. else i++;

   19. }

   20 return s.pop();

   21. }

   the expression can only contain unsigned integer numbers and + and - operators.

1. Rewrite only the lines of code that need to be changed so that the above function converts a postfix expression to a prefix expression.
2. Describe in words what changes are needed on the above given convert() function so that it also finds the value of the converted postfix expression.