Foundations of Computing UFCFFS-30-1

Portfolio Task 3 Due 23-12-2020 Mark /20

Based on the FA you already designed, your next task is to extend it to a Pushdown Automaton (PDA) which can recognise arithmetic expressions with brackets. All brackets must be paired up correctly. Multiplication operator cant be omitted.

Some accepted examples: 1, -2, -(1), (1+2)*(3-7.3), 1/(-3-1), 8*-(3/8), ((1.2))/(2.1)

Some rejected examples: (3)), (2)(3), 4-)(, (1.)5, ((3)3)

In Appendix, we show you an example of PDA which accepts strings of unary numbers with correctly matched brackets. Please fully understand how it works. When you design your PDA, you should use your FA (from previous worksheet) as a start point. You need to modify your FA into a PDA, thinking carefully where are the positions you should allow open/close brackets.

For full marks the diagram must be complete and correct in every respect.

This worksheet is worth of 30% this terms assignment.

The hand in date is Thursday 23rd of Dec 2020.

Appendix An Example of PDA

A simple example of PDA is a recogniser for the language

{ 1, 11, 111, (1), (1)(1), (1(11)), ((1)(1)11), }

Below is a possible PDA.

PTO

Task 2 model answer

Please use this as a start point for Portfolio task 3