Questions

Homework assignments must be done individually. Collaboration on homework assignments is not allowed.

Question 1:

Draw a deterministic finite-state machine that accepts the language of usernames defined as follows:

A username

• can include letters, digits, underscores ( _ ), and periods ( . )
• must start with a letter or underscore
• must include at least one letter or digit
• cannot have two (or more) periods in a row

Label the edges of your FSM with the characters _ and . (or use the word dot) and the words letter and digit.

Question 2:

Write a regular expression for the language of identifiers defined as follows:

An identifier

• can include dashes ( - ) and letters
• cannot have more than two dashes in a row
• must include at least one letter (i.e., one or two dashes alone are not legal identifiers)

You may use letter to mean any letter.

Handing in

Homework may be submitted electronically or on paper.

To hand in your homework electronically, follow the handin procedure to submit by 2:30 on Tuesday, September 16th, a file containing your answers in one of the following formats:

• a plain-text file named named H1.txt
• a pdf file named H1.pdf

To hand in your homework on paper,

• use standard-sized paper (e.g., 8.5 x 11 in)
• neatly print your name and CS login at the top of the first page
• if you have multiple pages, please staple all your pages together
• your work can be hand-written or a print-out of whatever format you prefer

Your paper submission can be turned in at lecture or put in Dillon Skeehan's mailbox on the 5th floor by 2:30pm on Tuesday, September 16th.