For every character in string

1. Looping through the characters of a std::string, using a range-based for loop (it's from C++11, already supported in recent releases of GCC, clang, and the VC11 beta):

   std::string str = ???;
   for(char& c : str) {
       do_things_with(c);
   }
   

2. Looping through the characters of a std::string with iterators:

   std::string str = ???;
   for(std::string::iterator it = str.begin(); it != str.end(); ++it) {
       do_things_with(*it);
   }
   

3. Looping through the characters of a std::string with an old-fashioned for-loop:

   std::string str = ???;
   for(std::string::size_type i = 0; i < str.size(); ++i) {
       do_things_with(str[i]);
   }
   

4. Looping through the characters of a null-terminated character array:

   char* str = ???;
   for(char* it = str; *it; ++it) {
       do_things_with(*it);
   }
   

A for loop can be implemented like this:

string str("HELLO");
for (int i = 0; i < str.size(); i++){
    cout << str[i];
}

This will print the string character by character. str[i] returns character at index i.

If it is a character array:

char str[6] = "hello";
for (int i = 0; str[i] != '\0'; i++){
    cout << str[i];
}

Basically above two are two type of strings supported by c++. The second is called c string and the first is called std string or(c++ string).I would suggest use c++ string,much Easy to handle.

In modern C++:

std::string s("Hello world");

for (char & c : s)
{
    std::cout << "One character: " << c << "\n";
    c = '*';
}

In C++98/03:

for (std::string::iterator it = s.begin(), end = s.end(); it != end; ++it)
{
    std::cout << "One character: " << *it << "\n";
    *it = '*';
}

For read-only iteration, you can use std::string::const_iterator in C++98, and for (char const & c : s) or just for (char c : s) in C++11.