String

    #define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstring>

using namespace std;

class String {
private:
    char* st;
    int size;
public:
    String();
    String(const char* s);
    String(const String&);
    ~String();
    void dislpay() const;
    void get();
    int lenght();
    String& operator=(const String&);
    friend String operator+(const String&, const String&);
    String& operator+=(const String&);
    bool operator==(const String&) const;
    bool operator!=(const String&) const;
    char& operator[](int);
    void operator()(int, int) const;
    friend istream& operator>>(istream&, String&);
    friend ostream& operator<<(ostream&, String&);
};

String::String() {
    this->size = 1;
    st = new char[this->size];
    st[0] = '\0';
    cout << "Был вызван конструктор: " << this << endl;
}
String::String(const char* s) {
    this->size = strlen(s) + 1;
    st = new char[this->size];
    strcpy(st, s);
    cout << "Был вызван конструктор: " << this << endl;
}
String::String(const String& other) {
    this->size = other.size + 1;
    this->st = new char[this->size];
    strcpy(this->st, other.st);
    cout << "Был вызван конструктор копирования: " << this << endl;
}
String::~String() {
    delete[] st;
    cout << "Был вызван деструктор: " << this << endl;
}
void String::dislpay() const {
    cout << "Строка: " << st << endl;
}
void String::get() {
    st = new char[80];
    cout << "Напишите строку: ";
    cin.getline(st, 80);
    int new_size = strlen(st) + 1;
    char* new_st = new char[new_size];
    strcpy(new_st, st);
    delete[] st;
    st = new_st;
    size = new_size;
}
int String::lenght() {
    return strlen(st);
}
String operator+(const String& s1, const String& s2) {
    String temp = s1;
    int new_size = s1.size + s2.size - 1;
    char* new_st = new char[new_size];
    strcpy(new_st, temp.st);
    delete[] temp.st;
    temp.st = new_st;
    strcat(temp.st, s2.st);
    temp.size = new_size;
    return temp;
}
String& String::operator=(const String& s) {
    delete[] st;
    st = new char[s.size];
    strcpy(st, s.st);
    size = s.size;
    return *this;
}
String& String::operator+=(const String& s) {
    int new_size = size + s.size;
    if (new_size >= size) {
        char* new_st = new char[new_size - 1];
        strcpy(new_st, st);
        delete[] st;
        st = new_st;
    }
    strcat(st, s.st);
    size = new_size - 1;
    return *this;
}
bool String::operator==(const String& s) const {
    if (!strcmp(st, s.st))
        return true;
    else return false;
}
bool String::operator!=(const String& s) const {
    if(!strcmp(st, s.st))
        return false;
    return true;
}
char& String::operator[](int index) {
    if (index >= size) {
        cout << "Ошибка!" << endl;
        exit(1);
    }
    return *(st + index);
}
void String::operator()(int start, int end) const {
    if (start < 0 || end >= size) {
        cout << "Ошибка!" << endl;
        exit(1);
    }
    cout << "Символы: ";
    for (int i = start; i <= end; i++)
        cout << *(st + i);
    cout << endl;
}
istream& operator>>(istream& in, String& s) {//################DON'T WORKED#######################
    return in >> s.st;
}
ostream& operator<<(ostream& out, String& s) {
    return out << s.st;
}

int main() {
    setlocale(LC_ALL, "Russian");
    String st1 = "Hello, ";
    String st2 = "World!";
    String st3;

    //st3 = "Hello, " + st2;
    //cout << st3 << endl;

    st3 = st1 + st2;
    cout << st3 << endl;

    return 0;
}