Stacks can be used for evaluating expressions.

*	Stacks use postfix expressions
*	Algorithm for evaluating a post fix expression using a stack

While there are tokens in the expression do
	get the next token
	if the token is an operator then
		retrieve and pop correct number of operands
	  	// first off the stack is the last operand
		do the operation and store results back on the stack
	else
		push the token on the stack
top of the stack has final answer

7 5 +
7 + 5 = 12
8 9 + 9 8 7 + 10 * + /
8 + 9 = 17
8 + 7 = 15
15 * 10 = 150
9+150=159
17/159=0.107
0.107

12 7  8  9  7  + *  4   4 / * / + = 12.05

*	Create a postfix expression from an infix expression
*	Need to know the priority

Operators have different priorities in stack and outside the stack

			In stack priority		In-coming priority
)					-				-
^					3				4
*,/					2				2
+, -					1				1
(					0				4

while true do
	if we are at the end of expression then
			print the stack and quit
	else
		if x is an operand then
			print x
		else if x = ')' then
			while top of the stack is not equal to '(' do
				retrievetop and pop from the stack 					
		and print the item retrieved
			pop '(' from the stack
		else 
			while the priority of the item on top of the
			stack is not less than priority of x do
				retrievetop and pop from the stack 					
		and print the item retrieved
			push x on the top of the stack
end {while}
X + C + U * Y^9 * (T + W * (7 + 8)) + A
(9+8)*6+((8+9)*7+8)*5
9 8 + 6 * 8 9 + 7 * 8 +5 *+
X C + U Y 9 ^ * T W 7 8 + * + * + A +