## prefix expression calculator

### What is prefix expression?

An prefix expression is a expression in which first operator comes and
proceded by strings. Every prefix string longer than a single variable
contains first and second operands followed by an operator.e.g.
**A,+A B ,*A B ,+ * A B/ C D**.

But in general expressions usually are in infix format.So, we have to
convert them into prefix expression.For that you can use
Infix to Prefix Converter .

### How to evaluate prefix expression?

1.First we read expression from right to left. So,During reading the
expression from right to left, push the element in the stack if it is
an operand.

2.If the current character is an operatorthen pop the two operands
from the stack and then evaluate it.

3.Push back the result of the evaluation. Repeat it till the end of
the expression.Checkout examples that are mention below in table

1) Postfix Expression: +54

Answer: 9

2) Postfix Expression: *94

Answer: 36

3) Postfix Expression:*+25+67

Answer:91

### Applications

As postfix evaluator is important and also has its advantage like that
prefix evaluator is somewhat similar but here operator positioning is
differnet but advantage will be same. Such as in calculators, in which
it scans and calculate expression value.