第八周项目4 String类的加减

/*
*Copyright (c) 2014,烟台大学计算机学院void change(int a[8][8]);
*All rights reserved.
*文件名称:main.cpp
*作者:苏强
*完成日期:2015年5月9日
*版本号:v1.0
*
*问题描述:请构造String类的加、减运算。其中，s1 + s2将两个字符串的连接起来；s1 - s2是将s1的尾部空格和s2的前导空格去除后的连接。
*/

#include <iostream>
#include <cstring>
using namespace std;

class String
{
public:
//需要的成员函数（若需要的话，声明友元函数）
String ();
String (char *c);
String (String &str);
~String ();
void display();
friend String operator + (String &s1,String &s2);
friend String operator - (String &s1,String &s2);
private:
char *p;   //指向存储的字符串
int len;   //记录字符串的长度
};
String::String ()
{
p=NULL;
len=0;
}
String::String (char *c)
{
len=strlen(c);
p=new char[len+1];
strcpy(p,c);
}
String::String (String &str)
{
len=str.len;
if(p!=NULL)    delete []p;
p=new char[len+1];
strcpy(p,str.p);
}
String::~String ()
{
if(!p) delete []p;
}
void String::display()
{
cout<<p<<endl;
}
String operator + (String &s1,String &s2)
{
String s;
s.len = s1.len+s2.len;
s.p = new char[s.len+1];   //原误写char(s.len+1)
strcpy(s.p,s1.p);
strcat(s.p,s2.p);
return s;
}

String operator - (String &s1,String &s2)
{
String s;
char *c1=new char[s1.len+1];
strcpy(c1,s1.p);
int i=s1.len-1;
while(i>=0&&c1[i]==' ')     --i;
c1[i+1]='\0';

char *c2=new char[s2.len+1];
strcpy(c2,s2.p);
i=0;
while(i<s2.len&&c2[i]==' ') ++i;
int j=0;
while(i<s2.len&&c2[i]!='\0')
{
c2[j]=c2[i];
++i;
++j;
}
c2[j]='\0';

s.len=strlen(c1)+strlen(c2);
s.p=new char[s.len+1];
strcpy(s.p,c1);
strcat(s.p,c2);
delete c1;
delete c2;
return s;
}
int main( )
{
String string1(" Hello  "), string2(" World ");
string1.display();
string2.display();
String string3;
string3 = string1 + string2;
string3.display();
string3 = string1 - string2;
string3.display();
return 0;
}