Question

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Task 1

Program a simple lexical analyzer that will build a symbol table from given stream of chars. You will need to read a file named "input.txt" to collect all chars. For simplicity, input file will be a C program without headers and methods. Then you will identify all the numerical values, identifiers, keywords, math operators, logical operators and others [distinct].

See the example for more details. You can assume that, there will be a space after each keywords. But, removal of space will add bonus points.

Input:

int a, b, c;
float d, e;
a = b = 5;
c = 6;
if ( a > b)
{
            c = a - b;
            e = d - 2.0;
}
else
{
            d = e + 6.0;
            b = a + c;
}

Output:

Keywords: int, float, if, else
Identifiers: a, b, c, d, e
Math Operators: +, -, =
Logical Operators: >
Numerical Values: 5, 6, 2.0, 6.0
Others: , ; ( ) { }

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Task 2

User will be asked first to input an integer value n followed by n lines of Strings. You have to find out whether it is an email or a web address or neither, along with its line number.

• You are not allowed to use any kind of built-in Regular Expression.
• The first part of a valid email address must start with a letter. But subsequent characters can be either letters or digits.
• The first part of a valid web address must be "www".
• The middle part of a valid email address (domain name; between the '@' and the '.') must not contain anything other than a letter.
• The middle part of a valid web address (domain name) must start with a letter. But subsequent characters can be either letters or digits.
• The 3rd (last) part of both a valid email and web address must be "com".

Input:

4
[email protected]
www.duh.com
www.thisIsAValidEmailAddress.com
[email protected]
3
[email protected]
www.validateYourEmails.com
http://www.nobodyLovesMe.com

Output:

Email, 1
Web, 2
Web, 3
Email, 4
None! 1
Web, 2
None! 3

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Task 3

Read a number from file, and then read that many lines of regular expressinos. The read another number and that many lines of string inputs. Match the RexEx patterns with the inputs and show if they matched or not by printing the sequence number (as read) of the pattern.

If one input matches multiple patterns, print all sequence numbers separated by commas.

Write your own RegEx parser. You must not use any built-in method or package for this.

For this task, you need to detect the following RexEx patterns. If you succeed, you may write a parser for all RegEx patterns.

Description	RE	Valid	Invalid
Zero or more	a(bc)*de	ade	abde
	abcbcde	abcbde
One or more	a(bc)+de	abcde	ade
	abcbcde	abc
Once or not at all	a(bc)?de	ade	abc
	abcde	abcbcde
Character classes	[a-m]*	blackmail	above
	imbecile	below
Negation of character classes	[^aeiou]	b	a
	c	e
Exactly N times	[^aeiou]{6}	rhythm	rhythms
	syzygy	syzygy

Input:

2
ab*c*d
a*b(cd)+e?f
3
acccd
abbbbbcccc
bcdcdef

Output:

YES, 1
NO, 0
YES, 2

Input:

3
[a-c]{3}cab+(da)*f
db*a[^def]{2}gh
def[k-p]*p+
5
defkmnpmpp
acbcabbf
pqrstdd
dbaabggh
dbbbbamkgh

Output:

YES, 3
YES, 1
NO, 0
NO, 0
YES, 2