Strings

1. Program to find the frequency of characters in a string(case insensitivity)
   Sample Input
   helloHowarEyou?
   Sample Output
   h - 2
   e - 2
   l - 2
   o - 3
   w - 1
   a - 1
   r - 1
   y - 1
   u - 1
   ? - 1
   
2. Program to remove special characters from string.
   Sample Input
   Training programs @ 4 placements
   Sample Output
   Trainingprogramsplacements
   
3. Program to find longest word in the given string.
   Sample Input
   Hello developers how are you
   Sample Output
   developers
   
4. Program to reverse of individual words in the given string.
   Sample Input
   Hello developers how are you
   Sample Output
   olleh srepoleved woh era uoy
   
5. Program to find highest frequency character in the given string.
   Sample Input
   hello developer how are you?
   Sample Output
   e 5
   
6. Program to replace a substring with another string in the given string.
   Sample Input
   hello world how are you
   world
   developer
   Sample Output
   hello developer how are you