i try to do this....i want to know if i use this program, is that correct?

Q:

How to write a java program taht evaluates a postfix expression by using concept of stack?

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Code:

public class PostfixEval
{
public static void main(String[] args)
{
TextIO.putln("This program can evaluate postfix expressions such as\n");
TextIO.putln(" 2 2 +");
TextIO.putln("or");
TextIO.putln(" 7.3 89.2 + 9 1.83 * 2 + /\n");
TextIO.putln("The operators +, -, *, /, and ^ can be used.\n\n");
while (true)
{
// Get and process one line of input from the user.
TextIO.putln("\n\n\nEnter a postfix expression or press return to end:\n");
TextIO.put("? ");
skipSpaces();
if (TextIO.peek() == '\n')
{
// If the line is empty (except for spaces), we are done.
break;
}
readAndEvaluate(); // Process the input.
TextIO.getln(); // Discard the end-of-line.
}
TextIO.putln("\n\nExiting program.");
} // end main();
static void skipSpaces()
{
// Skip past any spaces and tabs on the current input line.
// When this routine returns, the next character is either
// the end-of-line character, '\n', or is a non-blank.
while (TextIO.peek() == ' ' || TextIO.peek() == '\t')
{
TextIO.getAnyChar();
}
}
static void readAndEvaluate()
{
// Read one line of input and process it as a postfix expression.
// If the input is not a legal postfix expression, then an error
// message is displayed. Otherwise, the value of the expression
// is displayed. It is assumed that the first character on
// the input line is a non-blank. (This is checked in the
// main() routine.)
NumberStack stack; // For evaluating the expression.
stack = new NumberStack(); // Make a new, empty stack.
TextIO.putln();
while (TextIO.peek() != '\n')
{
if ( Character.isDigit(TextIO.peek()) )
{
// The next item in input is a number. Read it and
// save it on the stack.
double num = TextIO.getDouble();
stack.push(num);
TextIO.putln(" Pushed constant " + num);
}
else
{
// Since the next item is not a number, the only thing
// it can legally be is an operator. Get the operator
// and perform the operation.
char op; // The operator, which must be +, -, *, /, or ^.
double x,y; // The operands, from the stack, for the operation.
double answer; // The result, to be pushed onto the stack.
op = TextIO.getChar();
if (op != '+' && op != '-' && op != '*' && op != '/' && op != '^')
{
// The character is not one of the acceptable operations.
TextIO.putln("\nIllegal operator found in input: " + op);
return;
}
if (stack.isEmpty())
{
TextIO.putln(" Stack is empty while trying to evaluate " + op);
TextIO.putln("\nNot enough numbers in expression!");
return;
}
y = stack.pop();
if (stack.isEmpty())
{
TextIO.putln(" Stack is empty while trying to evaluate " + op);
TextIO.putln("\nNot enough numbers in expression!");
return;
}
x = stack.pop();
switch (op)
{
case '+': answer = x + y; break;
case '-': answer = x - y; break;
case '*': answer = x * y; break;
case '/': answer = x / y; break;
default: answer = Math.pow(x,y); // (op must be '^'.)
}
stack.push(answer);
TextIO.putln(" Evaluated " + op + " and pushed " + answer);
}
skipSpaces();
} // end while
// If we get to this point, the input has been read successfully.
// If the expression was legal, then the value of the expression is
// on the stack, and it is the only thing on the stack.
if (stack.isEmpty())
{ // Impossible if the input is really non-empty.
TextIO.putln("No expression provided.");
return;
}
double value = stack.pop(); // Value of the expression.
TextIO.putln(" Popped " + value + " at end of expression.");
if (stack.isEmpty() == false) {
TextIO.putln(" Stack is not empty.");
TextIO.putln("\nNot enough operators for all the numbers!");
return;
}
TextIO.putln("\nValue = " + value);
} // end readAndEvaluate()
} // end class PostfixEval

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Attached the question,i know for you is simple, but i really need your help...Thank you