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CBSE’s class XII computer science syllabus also happens to have infix to postfix conversions (and vice versa) as an application of a stack…without actually coding. Weird, or shall I say, good – because THAT sort of coding will knock the socks of most people. Anyway, I’ve given solutions to the conversion exercises given by our school. I hope they’re correct, and in case they aren’t, please do leave a comment to correct me.

Postfix, also known as the Reverse Polish Notation, is something some friends of mine have a called a pain in the butt. Indeed, if you try to follow the algorithm given in the notes given in our school, you’ll find the procedure is not that clear. Although it’s based on Djikistra’s ‘shunting yard’ algorithm, you’ll find that this explanation is WAY better the one given in our notes. The Sumita Arora book’s description is OK too, so you may go in for that if you’re physically incapable of making a small mouse click (and perfectly capable of lifting a heavy book).

Infix to Postfix
1. X + Y * Z ^ P – (X / Y + Z)

2. (A + B ^ D) / (E – F) + G

3. NOT (A OR B) AND C

4. ( !(TRUE && FALSE) || (TRUE || FALSE) )

Postfix to Infix
1. 20 8 4 / 2 3 + * –

2.* FALSE FALSE TRUE TRUE NOT AND TRUE AND OR AND

* Here, the given question is wrong because enough operands have not
been given for successful completion of algorithm. However, I decided
to put it up anyway so that the method could be demonstrated. Note that
if the last AND is removed, then the question becomes perfectly valid.