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 .

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

Answer: 9

2) Postfix Expression: *94

Answer: 36

3) Postfix Expression:*+25+67

Answer:91

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.