Eighth Week item four construction of the-string class

Please construct the add and subtract operations of the string class. where S1 + S2 connects two strings, S1-S2 is the connection that removes the trailing spaces of S1 and the leading spaces of the S2.
Tip: There are pointer members, which should be noted at design time. This, you know.

#include <iostream> #include <cstring>using namespace Std;class string{public:string ();    Default constructor String (const char *s);               String (string &str);    Constructor ~string ();    void display ();    Friend string operator + (string &s1,string &s2);    Friend string operator-(string &s1,string &s2);p Rivate:char *p;                                       int Len; A character pointer used to point to a string};    String::string () {len = 0; p = NULL;}    string::string (const char *s) {len = strlen (s);    p = new Char[len+1]; strcpy (p,s);}    String::string (String &str) {len = Str.len;   if (p!=null) delete []p;    When the assignment occurs, the original object may already exist, and the original space must be freed P = new char[len+1]; strcpy (P,STR.P);} String::~string () {if (!p) delete []p;} void string::d isplay ()//The string that the output p points to {Cout<<p<<endl;}    String operator + (string &s1, String &s2) {string S;    S.len = S1.len+s2.len;   S.P = new Char[s.len+1]; Original mis-write char (s.len+1)   strcpy (S.P,S1.P);    strcat (S.P,S2.P); return s;}    String operator-(string &s1, String &s2) {string S;    C1 string Char *c1=new char[s1.len+1] for the truncated trailing space;    strcpy (C1,S1.P);    int i=s1.len-1;    while (i>=0&&c1[i]== ")--I.;    c1[i+1]= ' + ';    C2 string char *c2=new char[s2.len+1] to remove leading whitespace;    strcpy (C2,S2.P);    i=0;    while (i<s2.len&&c2[i]== ') ++i;    int j=0;        while (i<s2.len&&c2[i]!= ') {c2[j]=c2[i];        ++i;    ++j;    } c2[j]= ' + ';    Connect the two parts S.len = strlen (c1) +strlen (C2);     S.P = new Char[s.len+1];    Original error Write char (s.len+1) strcpy (S.P,C1);    strcat (S.P,C2);    Delete C1;    Delete C2; return s;}    int main () {String string1 ("Hello"), string2 ("World");    String1.display ();    String2.display ();    String String3;    String3 = string1 + string2;    String3.display ();    String3 = string1-string2;    String3.display (); return 0;}

Operation Result:

Summary of Knowledge points:

To manipulate a string with a pointer

Please construct the add and subtract operations of the string class. where S1 + S2 connects two strings, S1-S2 is the connection that removes the trailing spaces of S1 and the leading spaces of the S2.
Tip: There are pointer members, which should be noted at design time. This, you know.
Learning experience:

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Eighth Week item four construction of the-string class