字符串类 class String

#include<iostream>
#include<string>
#include<stdlib.h>
#include<assert.h>
using namespace std;

class String{
private:
    char *str;
    int size;
public:
    String(char *s);
    ~String();
    String operator+(String& s);
    String operator=(String& s);
    String Substr(int index,int cout);
    int Find(char c,int start);
}

String::String(char *s)
{
    size=strlen(s);
    str=new char[size+1];
    assert(str!='\0');
    strcpy(str,s);
}

String::~String()
{
}

String String::operator+(String& s)//拼接
{
    String temp="\0";
    int len;
    len=size+s.size;
    delete [] temp.str;
    temp.str=new char[len+1];
    assert(temp.str!=NULL);
    temp.size=len;
    strcpy(temp.str,str);
    strcat(temp.str,s.str);
    return temp;
}

String String::operator=(String& s)//赋值
{
    if(size!=s.size)
    {
        delete[]str;
        str=new char[s.size+1];
        assert(str!=NULL);
        size=s.size;
    }
    strcpy(str,s.str);
    return *this;//返回得到的字符串
}

String String::Substr(int index,int count)//提取字符串 index开始下表 cout长度
{
    int i;
    int left=size-index;
    String temp=NULL;
    if(index>=size) return temp;
    if(count>=left) count=left;
    delete [] temp.str;
    temp.str=new char[count+1];
    assert(temp.str!=NULL);
    char *p,*q;
    p=temp.str;
    q=&str[index];
    for(int i=0;i<count;i++)
        *p++=*q++;
    *p='\0';
    temp.size=count;
    return temp;
}

int String::Find(char c,int start)
{
    int i=start;
    assert(i<size);
    while(str[i]!='\0'&&str[i]!='c')
    {
        i++;
    }
    if(str[i]=='\0')
        return -1;
    else
        return i;
}

void main()
{
    char *s;
    s="qweasd123";
    String::String(char *s);

    cout<<s;
    cou<<"12312312";

}