C++ Class Inheritance from String class

 
 #include <iostream>
 #include <cstring>                //for strcpy(), etc.
 using namespace std;
 class String                      //base class
 {
    protected:                     //Note: can't be private
    enum { SZ = 80 };           //size of all String objects
    char str[SZ];               //holds a C-string
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    String()                    //constructor 0, no args
    { str[0] = '\0'; }
    String( char s[] )          //constructor 1, one arg
    { strcpy(str, s); }      //  convert string to String
    void display() const        //display the String
    { cout << str; }
    operator char*()            //conversion function
    { return str; }          //convert String to C-string
 };
 class Pstring : public String     //derived class
 {
    public:
    Pstring( char s[] );        //constructor
 };
 Pstring::Pstring( char s[] )      //constructor for Pstring
 {
    if(strlen(s) > SZ-1)           //if too long,
    {
       for(int j=0; j<SZ-1; j++)   //copy the first SZ-1
          str[j] = s[j];           //characters "by hand"
       str[j] = '\0';              //add the null character
    }
    else                           //not too long,
       String(s);                  //so construct normally
 }
int main()
{                                        //define String
    Pstring s1 = "This is a very long string. This is a very long string. This is a very long string. This is a very long string. ";
    cout << "\ns1="; s1.display();           //display String
    Pstring s2 = "This is a short string.";  //define String
    cout << "\ns2="; s2.display();           //display String
    cout << endl;
    return 0;
}