Write a function called clean that takes a C++ string as input and removes any characters in the string that are not letters except for space blanks. code example

Example: Write a function called clean that takes a C++ string as input and removes any characters in the string that are not letters except for space blanks.

// ALWAYS USE PASS BY REFERENCE WITH STRINGS AND VECTORS.

void clean ( string & str)

{
   for ( int i = 0; i < str.length(); i++ )
   {
         if (str[i] != ' ' && (str[i] < 'A' || (str[i] > 'Z' && str[i] < 'a') || str[i] > 'z'))
         {
             str.replace(i, 1, "");
             i--;
         }
   }
}