81. Extract the domain name from an email address.
82. Reverse a string without using recursion.
83. Reverse a string using recursion.
84. Count the number of times a substring appears in a string.
85. Check if a string is a valid identifier.
86. Convert a string to a list of words.
87. Convert a list of words into a string.
88. Check if a string is in title case.
89. Reverse the first half of a string.
90. Reverse the second half of a string.
91. Check if two strings are rotations of each other.
92. Convert a string to binary.
93. Convert binary back to a string.
94. Find the longest consecutive sequence of a character in a string.
95. Remove all duplicate words in a string.
96. Extract the username from an email address.
97. Count the number of syllables in a string.
98. Split a string into two equal halves.
99. Check if a string can be converted to a palindrome by rearranging characters.
100. Swap the first and last characters of a string.
101. Find the longest substring without repeating characters.
102. Find the shortest substring that contains all unique characters.
103. Replace every vowel in a string with the next vowel.
104. Replace every consonant in a string with the next consonant.
105. Rotate a string by a given number of positions.
106. Remove all whitespace characters from a string.
107. Check if a string contains only printable characters.
108. Convert a string into a valid file name.
109. Convert a string into a valid URL.
110. Split a string into two parts at the first occurrence of a given character.
111. Find the middle character(s) of a string.
112. Check if a string is a valid phone number.
113. Capitalize the first letter of each sentence in a string.
114. Remove all vowels and count how many were removed.
115. Reverse the words in a string without changing the order of the characters.
116. Insert a substring into a string at a specific index.
117. Check if a string contains equal numbers of vowels and consonants.
118. Replace every letter in a string with its position in the alphabet.
119. Calculate the ASCII sum of all characters in a string.
120. Sort the characters in a string alphabetically.