Algorithm for infix to prefix conversion?

Answer 1

Algorithm to Convert Infix to Prefix Form

Suppose A is an arithmetic expression written in infix form. The algorithm finds equivalent prefix expression B.

Step 1. Push ")" onto STACK, and add "(" to end of the A

Step 2. Scan A from right to left and repeat step 3 to 6 for each element of A until the STACK is empty

Step 3. If an operand is encountered add it to B

Step 4. If a right parenthesis is encountered push it onto STACK

Step 5. If an operator is encountered then:

a. Repeatedly pop from STACK and add to B each operator (on the top of STACK) which has same or higher precedence than the operator.

b. Add operator to STACK

Step 6. If left parenthesis is encontered then

a. Repeatedly pop from the STACK and add to B (each operator on top of stack until a left parenthesis is encounterd)

b. Remove the left parenthesis

Step 7. Exit

Answer 2

Basically, the shunting algorithm (infix to postfix) works like this (I'm writing this from memory, BTW, so I apologize in advance for any mistakes):
1. You create a stack and an output string.
2. Then you read the infix string one token at a time; each token is either an identifier or an operator:
a. If the token is an identifier (eg, a variable or a constant), then you append it onto the end of the output string.
b. If the token is an operator, then you compare its precedence with the precedence of the operator on the top of the stack.
i. If the operator on the top of stack has lower precedence, then push the new operator onto the stack.
ii. Else, pop the operator from the top of stack and append it to the output string. Then push the new operator onto the stack.
otherwise
c. If the token is an open parenthesis, then push it onto the stack.
d. If the token is a close parenthesis, then pop and append the operators from the stack until the open parenthesis is popped. Discard both parentheses.

Google for "shunting algorithm" for a more detailed and better better description. You might also find reference to an algorithm for converting infix to prefix.
Algorithm_for_infix_to_prefix_conversion

refer this page for your question.....

Answer 3

Infix: "1 + 2"
Prefix: "+ 1 2"
Postfix: "1 2 +"

The difference is where you put the operator: Betweeen (infix), before (prefix) or after (postfix) the arguments you operate on.