Assignment 4 Regex

Programming Assignment 4 Regex
Problem 1
Abstract
In this assignment, we begin to use the searching language Regex to search for strings or keywords withing
a data set. Regex is a very powerful and useful language to know. In this assignment I have written the
correct Regex expressions to find the keys inside a string that was assigned to us.
3)
a) What is stored in ”matches”?
The variable matches contains all the matches keys found from the string by using the correct regex notation.
It is an array that contains all the found instances of the keys.
b) What does \d ”mean?
”\d” is Regex code for a digit character. In our case, the code will find the first instance of one digit
character. If we use the input string ”I would like the number 98”” to be found and printed, thanks.”, then
our regex match will be ”9”.
c) What does ”\d ”mean?
To correctly modify my expression for the Regex, I used the following code:
Figure 1: Code used for Regex pattern, part 1.
This displays the following output on the terminal:
Figure 2: Output on term
It is interesting to note that three strings were grabbed during this process, but the second and third string
do match the required strings.
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Robert Quan COMPSCI 221 (Dr. Leyk ): Programming Assignment 4 Regex Problem 1
Problem 2
a) What does ”\s\S”mean?
backslashs is the Regex code for a whitespace character to be found and backslashS denotes any character
that is NOT a whitespace. An example of this would be any space and then the first letter of the next word
would be taken as an entry to our matches array.
b) What is stored inside matches[0]?
Our matches array will find any matching regex code to our string. Inside of matches[0], while using the
given regex statment, we have ” < title This is a title< /title ”. The matching is case sensitive. This
first Capturing Group matches the characters < title literally and any character up to < \title in our
first capturing group.
c) Why is matches[1] different?
Matches[1] contains the string ”This is a title”. We can see that it excluded the < title and < /title
this is because of the sub group that we put in ([\s\S]+). The second capturing group has a Quantifier that
matches between one and unlimited times.
d) Modify the Regex code
After modifying the Regex pattern to retrieve only the items indide of the header tag but not inside the title
tag, I ended up writing this pattern:
Figure 3: Code used for Regex pattern, part 2.
This displays the following output on the terminal:
Figure 4: Output on term
An interesting note on this pattern is that I had to print out the second and fourth match on out matches
array. This is because I used a Capturing group which had a total of 4 group matching.
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Robert Quan COMPSCI 221 (Dr. Leyk ): Programming Assignment 4 Regex Problem 2
Problem 3
a) Write a program using regex that will go through the text file and print out the file name of every hyperlinked powerpoint file.
For this problem, I created a fstream object that read in the stroustrup.txt file. After writing the correct
pattern to search for, I found the output by setting the matches into a string object and then checking
whether the size was bigger than 0 characters in length. This successful printed out the filenames I needed.
The code and output are the following:
Figure 5: Pattern for stroustrup.txt
Figure 6: Output on term
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