Regular expressions for token patterns in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to match an identifier starting with a letter followed by letters or digits.

Compiler Design

pattern = r"[1]"

Drag options to blanks, or click blank then click option'

A"\d+"

B"[0-9]+"

C"[a-zA-Z][a-zA-Z0-9]*"

D"[a-z]+"

Attempts:

3 left

💡 Hint

Common Mistakes

Using digits at the start of the pattern

Not allowing digits after the first character

The pattern [a-zA-Z][a-zA-Z0-9]* matches an identifier that starts with a letter and is followed by zero or more letters or digits.

2fill in blank

medium

Complete the regular expression to match an integer literal consisting of one or more digits.

Compiler Design

pattern = r"[1]"

Drag options to blanks, or click blank then click option'

A"[a-zA-Z]+"

B"[0-9]*"

C"[a-z]+"

D"[0-9]+"

Attempts:

3 left

💡 Hint

Common Mistakes

Using * which allows zero digits

Using letters instead of digits

The pattern [0-9]+ matches one or more digits, which is suitable for integer literals.

3fill in blank

hard

Fix the error in the regular expression to correctly match a floating-point number with optional decimal part.

Compiler Design

pattern = r"\d+[1]\d*"

Drag options to blanks, or click blank then click option'

A"."

B"\."

C"\\."

Attempts:

3 left

💡 Hint

Common Mistakes

Not escaping the dot, causing it to match any character

Using too many backslashes

The dot . is a special character in regex that matches any character. To match a literal dot, it must be escaped as \..

4fill in blank

hard

Fill both blanks to create a regex that matches an identifier starting with a letter and containing letters, digits, or underscores.

Compiler Design

pattern = r"[1][2]*"

Drag options to blanks, or click blank then click option'

A"[a-zA-Z]"

B"[0-9]"

C"[a-zA-Z0-9_]"

D"[_]"

Attempts:

3 left

💡 Hint

Common Mistakes

Allowing digits or underscores as the first character

Not including underscore in the second part

The first blank matches the first letter [a-zA-Z]. The second blank matches zero or more letters, digits, or underscores [a-zA-Z0-9_]*.

5fill in blank

hard

Fill all three blanks to create a regex that matches a string literal enclosed in double quotes, allowing escaped quotes inside.

Compiler Design

pattern = r"\"[1][2]*[3]\""

Drag options to blanks, or click blank then click option'

A"(\\.|[^"]"

B"(\\.|[^"])*"

Attempts:

3 left

💡 Hint

Common Mistakes

Not escaping quotes inside the string

Not matching zero or more characters inside quotes

The pattern matches a double quote, then zero or more occurrences of either an escaped character (like \"), or any character except a double quote, and finally a closing double quote.