[求助]内存分配问题

以下两个程序输出的结果为何不一样：请指点一二

程序1：
#include<iostream.h>
#include<string.h>
#include<malloc.h>
void main()
{
char *pstr;
pstr=(char *)malloc(100);
strcpy(pstr,"hello");
//cout<<pstr<<endl;
free(pstr);
if(pstr!=NULL)
{
strcpy(pstr,"world");
}

cout<<pstr<<endl;
}


程序2：
#include<iostream.h>
#include<string.h>
#include<malloc.h>
void main()
{
char *pstr;
pstr=(char *)malloc(100);
strcpy(pstr,"hello");
cout<<pstr<<endl;
free(pstr);
if(pstr!=NULL)
{
strcpy(pstr,"world");
}

cout<<pstr<<endl;
}