程序的来源是《c primer plus》第十一章第10题，这里面我不懂的是if ( gets(str[n]) == NULL ) break;后为什么不直接使用输入的str[]字符串，而是现将str[]地址赋给p[]，p[]=str[];  求指教！！！
部分程序如下：

int main(void)
{
    char str[10][81];

 char *p[10];

 char command[10];

 int n;

 while(1)

 {
  n = 0;
  puts("input no more than 10 strings finished by EOF (^Z):");
  do
  {
   if ( gets(str[n]) == NULL ) break;
   p[n] = str[n];
   n++;
  }
  while( n<10 );
  puts("select:");
  puts("a. put originally");
  puts("b. put in order of ascii");
  puts("c. put in order of string's length");
  puts("d. put in order of first word's length");
  puts("e. input strings again");
  puts("q. quit");
  do
  {
   gets(command);
   switch(command[0])
   {
   case 'a': puts("put originally:");      origin_put(p,n); break;
   case 'b': puts("put in order of ascii:");     ascii_put(p,n);  break;
   case 'c': puts("put in order of string's length:");  length_put(p,n); break;
   case 'd': puts("put in order of first word's length:"); word_put(p,n);   break;
   case 'e': break;
   default :   puts("Quit.");  return 0;
   }
  }
  while( command[0] != 'e' );


 }
}