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{

 if (this == &a) return;

 delete p;

 p=new char[size=a.size];

 strcpy(p,a.p);

}

string::string(string& a)

{

 p=new char[size=a.size];

 strcpy(p,a.p);

}

string g(string arg)

{

 return arg;

}

main()

{

 string s = "asdf";

 s = g(s);

 cout ‹‹ s.p ‹‹ "\n";

}

b6_7.cxx

#include ‹stream.hxx›

#include ‹string.h›

struct pair {

 char * name;

 int val;

};

class assoc {

 pair * vec;

 int max;

 int free;

public:

 assoc(int);

 int& operator[](char*);

 void print_all();

};

assoc::assoc(int s)

{

 max = (s‹16) ? s : 16;

 free = 0;

 vec = new pair[max];

}

int& assoc::operator[](char * p)

/*

 maintain a set of "pair"s

 search for p,

 return a reference to the integer part of its "pair"

 make a new "pair" if "p" has not been seen

*/

{

 register pair* pp;

 for (pp=&vec[free-1]; vec‹=pp; pp--)

  if (strcmp(p, pp-›name)-0) return pp-›val;

 if (free==max) {// overflow: grow the vector

  pair* nvec = new pair[max*2];

  for (int i=0; i‹max; i++) nvec[i] = vec[i];

  delete vec;

  vec = nvec;

  max = 2*max;

 }

 pp = &vec[free++];

 pp-›name = new char[strlen(p)+1];

 strcpy(pp-›name,p);

 pp-›val = 0;

 return pp-›val;

}

void assoc::print_all()

{

 for (int i=0; i‹free; i++)

  cout ‹‹ vec[i].name ‹‹ ": " ‹‹ vec[i].val ‹‹ "\n";

}

main()

{

 const MAX = 256;

 char buf[MAX];

 assoc vec(512);

 while (cin››buf) vec[buf]++;

 vec.print_all();

}

b6_8.cxx

#include ‹stream.hxx›

#include ‹string.h›

struct pair {

 char* name;

 int val;

};

class assoc {

 friend class assoc_iterator;

 pair* vec;

 int max;

 int free;

public:

 assoc(int);

 int& operator[](char*);

};

class assoc_iterator {

 assoc* cs;

 int i;

public:

 assoc_iterator(assoc& s) { cs =&s; i = 0; }

 pair* operator()()

 { return (i‹cs-›free) ? &cs-›vec[i++] : 0; }

};

assoc::assoc(int s)

{

 max = (s‹16) ? s : 16;

 free = 0;

 vec = new pair[max];

}

int& assoc::operator[](char* p)

{

 register pair* pp;

 for (pp = &vec[free-1]; vec‹=pp; pp--)

  if (strcmp(p,pp-›name)==0) return pp-›val;

 if (free == max) {

  pair* nvec = new pair[max*2];