class String

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
class String{
    int _size;
    char * _str;
public:
    String();
    String(const char *);
    String(const String&);
    ~String();
    String& operator =(const String&);
    String& operator =(const char*);
    void operator -=(const char*);
    void operator -=(const String&);
    void operator +=(const char*);
    void operator +=(const String&);
    vector<int> allPos(const char*);
    int removeStr(const char*);
    void add(const char*);
    int getSize();
    char* getStr();
};

vector<int> String::allPos(const char* str){
    vector<int> v; int len = strlen(str);
    for (int i = 0, j = 0; i < _size; ++i){
        if ( _str[i] == str[j] ){
            j++;
            if ( j == len ) {
                v.push_back(i-j+1);
                --i;
            }
        } else j = 0;
    }
    return v;
}

void String::operator +=(const char* str){
    add(str);
}

void String::operator +=(const String& str){
    add(str._str);
}

void String::add(const char* str){
    _size += strlen(str);
    char* temp = new char[_size+1];
    strcpy(temp,_str);
    strcat(temp, str);
    temp[_size] = '\0';
    delete [] _str;
    _str = temp;
}

void String::operator -=(const char* str){
    removeStr(str);
}

void String::operator -=(const String& str){
    removeStr(str._str);
}

int String::removeStr(const char * str){
    auto v = allPos(str);

    for(int i = v.size()-1, len = strlen(str); i >= 0; --i){
        _size -= len;
        for(int j = v[i]; j < _size; j++){
            _str[j]=_str[j+len];
        }
    }

    if ( v.size() != 0 ) {
        char* temp = new char[_size+1];
        strncpy(temp, _str, _size);
        temp[_size] = '\0';
        delete [] _str;
        _str = temp;
    }

    return v.size();
}

int String::getSize(){return _size;}
char* String::getStr(){return _str;}

String::String(){
    _size = 0;
    _str = 0;
}

String::String(const char* str){
    if (!str){
        _size = 0; _str = 0;
    } else {
        _size = strlen (str);
        _str = new char [_size +1];
        strcpy(_str, str);
    }
}

String::String(const String& str){
    _size = str._size;
    if ( !str._str ){
        _str = 0;
    } else {
        _str = new char[_size +1];
        strcpy(_str, str._str);
    }
}

String::~String(){
    delete [] _str;
}

String& String::operator=( const char * str ){
   if ( ! str ) {
     _size = 0;
     delete [] _str;
     _str = 0;
   } else {
     _size = strlen( str );
     delete [] _str;
     _str = new char[ _size + 1 ];
     strcpy( _str, str );
   }
   return *this;
}

String& String::operator=( const String & str)
{
   if ( this != & str) {
      delete [] _str;
      _size = str._size;
      if ( ! str._str )
         _str = 0;
      else {
         _str = new char[ _size + 1 ];
         strcpy( _str, str._str );
      }
   }
   return *this;
}

int main(){
    String s1("hello");
    String s2("_world");
    for (int i = 0; i < 10; ++i)
        s1 += s2;
    cout<< "s1 = "<<s1.getStr()<<endl;
    cout<< "size s1 = " << s1.getSize()<<endl;
    s1 -= "wor";
    cout<< s1.getStr()<<endl;
}