A simple implementation case of a string class

class String
{
	public:
		String()
		{
			data = new char[1];  //Why use new char[1] here? Although it is a character, this is to keep symmetric with the destructor, because the char[] is used in other constructors			data[0]='\0';
			length = 0;
		}
		String(const char* str)
		{
			length = strlen(str);
			data = new char[length+1];
			strcpy(data,str);
			data[length]='\0';
		}
		String(const char* str,int n)
		{
			length = n;
			data = new char[n+1];
			strncpy(data,str,n);
			data[length] ='\0';
		}
		String(const String& src) //Copy constructor, that is, copy constructor		{
			length = ;
			data = new char[length+1];
			strcpy(data,);
		}
		String& operator=(const String& src) //Assignment constructor		{
			if(this == &src)
				return *this;
			delete [] data;
			data = new char[+1];
			strcpy(data,);
			return *this;
		}
		String& operator=(const char* src) //Another assignment constructor		{
			delete [] data;
			length = strlen(src);
			data = new char[length+1];
			strcpy(data,src);
			return *this;
		}
		char& operator[](int n)
		{
			return data[n];
		}
		const char& operator[](int n) const  //For const member functions, it is best to return a reference to const, so as to avoid the return value being modified		{
			return data[n];
		}
	friend	ostream& operator<<(ostream& os,const String& st)； 
		 
		~String()
		{
			delete [] data;	
		}
	private:
		char* data;
		int length;	
};
ostream& operator<<(ostream& os,const String& st)
{
   os<<;
  return os;
}