I have problem in counting the number of letters in the strings entered by the user. CAn anyone suggest something in the following codes?

Why not use a string
Add
#include <string> at the top
replace char* ... with this
std::string str; // and
and change your output line to this....
std::cout<<"Length == "<<str.length()<<std::endl;
note that since string is a class, and str is an object of type string,
you call the string method called length. It is not a variable of string but a function hence the () after length.

However, it you want to count the letters and be a bit more careful about
spaces etc. Then there a a lot of post here and FAQs elsewhere that discuss how to proceed.

Replace:
char *str; with
string str;
and fix:
str.length with
str.length()