1. Write a function to reverse a string.

2. Implement a function to check if a string is a palindrome.

3. Write a function to find the length of a string.

4. Implement a function to count the number of vowels in a string.

5. Write a function to count the number of consonants in a string.

6. Implement a function to count the number of words in a string.

7. Write a function to convert a string to uppercase.

8. Implement a function to convert a string to lowercase.

9. Write a function to capitalize the first letter of each word in a string.

10. Implement a function to find the frequency of each character in a string.

11. Write a function to remove all white spaces from a string.

12. Implement a function to remove all occurrences of a given character from a string.

13. Write a function to check if two strings are anagrams.

14. Implement a function to replace all spaces in a string with a given character.

15. Write a function to find the first non-repeating character in a string.

16. Implement a function to find the last non-repeating character in a string.

17. Write a function to check if a string contains only digits.

18. Implement a function to check if a string contains only alphabets.

19. Write a function to check if a string contains only alphanumeric characters.

20. Implement a function to find the longest word in a string.

21. Write a function to find the shortest word in a string.

22. Implement a function to count the occurrences of a given character in a string.

23. Write a function to find the first occurrence of a substring in a string.

24. Implement a function to find the last occurrence of a substring in a string.

25. Write a function to check if a string starts with a given substring.

26. Implement a function to check if a string ends with a given substring.

27. Write a function to split a string into an array of words.

28. Implement a function to join an array of words into a single string.

29. Write a function to remove duplicate characters from a string.

30. Implement a function to find the most frequent character in a string.