string and const in C and C++

#include <iostream>
#include <string>
using namespace std;

int main()
{
  const char *st = "12";

  cout << sizeof(st) << endl; //print the size of pinter!

  string s1 = "123";

  cout << sizeof(s1) << endl; //still not the actual length
  cout << s1.size() << endl; //number of characters, excluding '\0'

  cout << s1.length() << endl;//same
  cout << strlen(s1.c_str()) << endl; //same


  cout << sizeof("123") << endl; //print 4, including '\0'
  //convert C++ string to C string
  char *not_right = s1.c_str();  //compile error, s1.c_str() is type
                                   //  (const char*) not (char*)

  //--------------------------------------------------
  // C-style strings  
  //p.90, B.S.


  char s[] = "asdf";
  cout << strlen(s) << endl; //print 4, excluding '\0'

  cout << sizeof(s) << endl; //print 5, includeing '\0'
 
  char *weird = "Trick or treat?"; //implicit const_cast by c++
                                   //for c compatibility or we will
                                   //break million lines of code

  
  weird[1] = 'a'; //error: assignment to const; result is undefined

  //if you really want to modifiy it, 
  //make the string guarantee to be able to modify
  char p[] = "ok now";

  p[0] = 'a'; //ok!  
}