#include<iostream.h>
#include<assert.h>
//----------------------------------------主串類
///////////////////////////
char nothing;
class string{
public:
	string();
	string(char);
	string(unsigned );
	string(const char*);
	string(const string &);
	~string();
	friend class substring;
	void operator=(const string & right);//賦值
	void operator+=(const string & right);////賦值用于串連接
    friend 	string operator+(const string & a,const string & b);//串連接
	istream & getline (istream &);//輸入
    friend	istream & operator>>(istream & in,string & str);
	operator const char *()const;//強制轉(zhuǎn)換類型為C字符
	int compare (const string &)const;	//比較字符
	friend int operator>(const string & ,const string & );
	friend int operator>=(const string & ,const string & );
	friend int operator<(const string & ,const string & );
	friend int operator<=(const string & ,const string & );
	friend int operator==(const string &,const string & );
	friend int operator!=(const string & ,const string & );
	substring operator ()(unsigned start,unsigned ien);//取子串
	char & operator[](unsigned index)const;//訪問單個字符
	unsigned length()const;//測量字符串的長度.
private:
	unsigned buflen;
	char *buffer;
};
//串長度
unsigned cstrlen(const char str[])
{
	unsigned i=0;
	while(str[i]!='\0')i++;
	return i;
}
//- - - - - - - - - - - - - - -創(chuàng)建一個空字符串
string::string()
{ buflen=1;
	buffer=new char[buflen];
	assert(buffer!=0);
	buffer[0]='\0';
}
// ---------------------------------------建立一個單字符的字符串
string::string(char c)
{ buflen=2;
	buffer=new char[buflen];
	assert(buffer!=0);
	buffer[0]=c;
	buffer[1]='\0';
}
//---------------------------------------構(gòu)造一個構(gòu)造函數(shù)分配一個緩沖區(qū)間
string::string(unsigned size)
{
	assert(size>=0);
	buflen=1+size;
	buffer=new char[buflen];
	assert(buffer!=0);
	for(unsigned i=0;i<buflen;i++)
		buffer[i]='\0';
}
//-----------------------------------------------
string::string(const char *s)
{
	buflen=1+cstrlen(s);
	buffer=new char[buflen];
	assert(buffer!=0);
	for(unsigned i=0;s[i]!='\0';i++)
		buffer[i]=s[i];
	buffer[i]='\0';
}
//------------------------------------//拷貝構(gòu)造
string::string(const string & s)
{
	buflen=1+cstrlen(s.buffer);
	buffer=new char[buflen];
	assert(buffer!=0);
	for(unsigned i=0;s.buffer[i]!='\0';i++)
		buffer[i]=s.buffer[i];
	buffer[i]='\0';
}
//-----------------	析構(gòu)函數(shù)
string::~string()
{
	delete[]buffer;
	buffer=NULL;
	buflen=0;
}
//------------------------------------
	string::operator const char *()const//強制轉(zhuǎn)換類型為C字符
	{
		return buffer;
	}
	//---------------------------------------
void string::operator =(const string & right)//賦值函數(shù)
{	
	const unsigned rightlength=right.length();
	if(right.length()>=buflen)
	{
		delete[]buffer;
	buflen=1+rightlength;
	buffer=new char[buflen];
	assert(buffer!=0);
}
	for(unsigned i=0;right.buffer[i]!='\0';i++)
		buffer[i]=right.buffer[i];
	buffer[i]='\0';
}
//---------------------------------------
void string::operator+=(const string & s)//賦值用于串連接
{
	unsigned i;
	unsigned conlen=length()+s.length();
	if(conlen>=buflen)
	{char * newbuf=new char[1+conlen];
	assert(newbuf!=0);
	for(i=0;buffer[i]!='\0';i++)
	newbuf[i]=buffer[i];
	delete[]buffer;
	buflen=1+conlen;
	buffer=newbuf;
	}
	else 
		i=cstrlen(buffer);
	for(unsigned j=0;s.buffer[j]!='\0';j++,i++)
		buffer[i]=s.buffer[j];
	buffer[i]='\0';
}
//---------------------------------------
string operator+(const string & left,const string & right)//串連接
{
	string result(left);
	result+=right;
	return result;
}
//--------------------------------------
unsigned string::length()const//測量字符串的長度
{
	return cstrlen(buffer);
}
//----------------------------------------
istream & string::getline(istream & in)//輸入和輸出
{char str[80];
	in.getline(str,80,'\n');
	string s1(str);
	*this=s1;
	return in;
}
//-----------------------------------------
istream & operator>>(istream & in,string & str)//輸入
{
	char inbuffer[1000];
	if(in>>inbuffer)
		str=inbuffer;
	else 
		str="";
	return in;
}
//-------------------------------------
int string::compare (const string & s)const//比較運算
{
	char *p=buffer;
	char *q=s.buffer;
	for(;(*p!='\0')&&(*p==*q);p++,q++)
		;
	return *p-*q;
}
int  operator<=(const string & a,const string & b)
{ 

	int result=a.compare(b);
	if(result<=0)
	return 1;
	else return 0;
}
int operator>(const string & a,const string & b)
{ 
int result=a.compare(b);
	if(result>0)
	return 1;
	else return 0;
}
int operator>=(const string & a,const string & b)
{ 
int result=a.compare(b);
	if(result>=0)
	return 1;
	else return 0;
}
int operator<(const string & a,const string & b)
{ 
int result=a.compare(b);
	if(result<0)
	return 1;
	else return 0;
}
int operator==(const string & a,const string & b)
{ 
int result=a.compare(b);
	if(result==0)
	return 1;
	else return 0;
}
//--------------------------------------------------
char & string::operator[](unsigned index)const//訪問單個字符
{
	if(index<0||index>cstrlen(buffer))
	{
		nothing='\0';
		return nothing ;
	}
	return buffer[index];
}