+-+

//+-=#include<iostream.h>#include<string.h>class string{protected: char *sp;public: string(){sp=0;}   string(string &); string(char *s)   {  sp=new char[strlen(s)+1];  strcpy(sp,s); } ~string (){if(sp)delete sp;}  void show(){cout<<sp<<endl;} string & operator = (string &);   friend string operator + (string &,string &);  string operator - (string &);  string operator - (char);    int operator > (string &);   };string::string(string &s){ if(s.sp){  sp=new char[strlen(s.sp)+1];  strcpy(sp,s.sp); } else  sp=0;}string operator + (string &s1,string &s2){ string t; t.sp=new char[strlen(s1.sp)+strlen(s2.sp)+1]; strcpy(t.sp,s1.sp);   strcat(t.sp,s2.sp);   return t;}string string::operator - (string &s){ string t1=*this; char *p; while(1) {  if(p=strstr(t1.sp,s.sp))      {    if(strlen(t1.sp)==strlen(s.sp))     {    delete t1.sp;        t1.sp=0;         break;          }   string t2;   t2.sp=new char[strlen(t1.sp)-strlen(s.sp)+1];   char *p1=t1.sp,*p2=t2.sp;   int i=strlen(s.sp);   while(p1<p) *p2++=*p1++;   while(i){p1++;i--;}      while(*p2++=*p1++);     t1=t2;  }  else break; } return t1;}string string::operator - (char s){ string t1; int i=0,flag=0; t1.sp=new char[strlen(sp)+1]; char *p1=sp,*p2=t1.sp; while(*p1) {  if(*p1!=s){   *p2++=*p1++;   i++;   flag=1;  }  else p1++; } *p2='\0'; return t1;}int string::operator > (string &s){ if(strcmp(sp,s.sp)>0)   {  return 1; } else return 0;}string & string::operator = (string &s) { if(sp) delete sp;  if(s.sp) {  sp=new char[strlen(s.sp)+1];   strcpy(sp,s.sp); } else sp=0; return *this;}void main(){ string s1("southeast"),s2("as"),s3,s4,s5; s1.show(); s2.show(); s3=s1+s2; s3.show(); if(s1>s2)  cout<<"s1>s2成立!"<<endl; else  cout<<"s1>s2不成立!"<<endl; s4=s3-s2; s4.show(); s5=s3-'t'; s5.show();}