Shaheer Harris

$6$:$27$PM $(0$ minutes ago$)$

to me

$19\mathrm{.}13$

$($Postfix: Evaluation$)$ Write a program that evaluates a valid postfix expression such as $62+5*84/-$

The program should read a postfix expression consisting of digits and operators into a string.

Using modified versions of the stack functions implemented earlier in this chapter, the program should scan the expression and evaluate it$.$ The algorithm is as follows:

$$While you have not reached the end of the string, 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 $\text{'}$O$\text{'}$ 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.

$$When you reach the end of the string, pop the top value of the stack. This is the result of the postfix expression.

$($Note: In Step $2$ above, if the operator is $\text{'}/\text{'},$ 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 $\text{'}-\text{'}.]$ The arithmetic operations allowed in an expression are

$+$ addition subtraction

$*$ multiplication

$/$

division exponentiation

$\%$ remainder

Nox: We assume left$-$to$-$right associativity for all operators for the purpose of this exercise.$|$ The rack should be maintained with stack nodes that contain an int data member and a pointer to the nar stack node. You may want to provide the following functional capabilities:

$$function evaluatePostfixExpression that evaluates the postfix expression

$$function calculate that evaluates the expression op$1$ operator op$2$

$$function push that pushes a value onto the stack

$$function pop that pops a value off the stack

$$function isEmpty that determines if the stack is empty

$$function printStack that prints the stack