There are many standard string functions already. You can create one more
B. Alphanumeric characters:
Alphanumeric characters refer all letters A-Z, a-z and digits 0-9. All other characters are non-alphameric.
Create a function to remove all non-alphanumeric characters and return the "cleaned" string.
In main(), let the user enter a string from the keyboard, call the function to clean up the string and print it out.