(Postfix Evaluator)Write a program that evaluates a postfix expression (assume it’s valid)...

(Postfix Evaluator)Write a program that evaluates a postfix expression (assume it’s valid) such as

6 2 + 5 * 8 4 / -

The program should read a postfix expression consisting of single digits and operators into a character array. Using the stack functions implemented earlier in this chapter, the program should scan the expression and evaluate it. The algorithm is as follows:

1) Append the null character ('\0') to the end of the postfix expression. When the null

character is encountered, no further processing is necessary.

2) While '\0' has not been encountered, read the expression from left to right.

If the current character is a digit,

Push its integer value onto the stack (the integer value of a digit character is its

value in the computer’s character set minus the value of '0' in the

computer’s character set).

Otherwise, if the current character is an operator,

Pop the two top elements of the stack into variables x and y.

Calculate y operator x.

Push the result of the calculation onto the stack.

3) When the null character is encountered in the expression, pop the top value of the stack.

This is the result of the postfix expression.

[Note: In 2) above, if the operator is '/', the top of the stack is 2, and the next element in the stack is 8, then pop 2 into x, pop 8 into y, evaluate 8 / 2, and push the result, 4, back onto the stack. This note also applies to operator '-'.]

The arithmetic operations allowed in an expression are:

+ addition- subtraction* multiplication/ division^ exponentiation% remainder