Solution to Homework 8

Solution to Problem 1

#include <iostream.h>
#include <fstream.h>
#include "mystring.h"
//copy the rest of the file into target file
void copyfile( ifstream &input, ofstream &output )
{  
    string str;
    while( input >> str )
          output << str << endl;
}

int main()
{
   ifstream f1, f2;
   ofstream f3;
   string a, b;
   f1.open( "names1.dat" );
   f2.open( "names2.dat" );
   f3.open( "names3.dat" );
   //read the first names from both files   
   f1 >> a;
   f2 >> b; 
   while( 1 ) {
     if( a > b )
       {
       f3 << b << endl;
       if ( !( f2 >> b ) )
       {
          f3 << a << endl;
          copyfile( f1, f3 );
          return 0;
        }
       }
     else if( a < b )
        {
        f3 << a << endl;
        if( !( f1 >> a ) )
         {
          f3 << b << endl;
          copyfile( f2, f3 );
          return 0;
          }
        }
     else
        {
        f3 << a << endl;
        if( !( f1 >> a ) )
         {
          f3 << b << endl;
          copyfile( f2, f3 );
          return 0;
          }
        if (!( f2 >> b ) )
         {
          f3 << a << endl;
          copyfile( f1, f3 );
          return 0; 
          }
       }
  }
}

Solution to Problem 2

6.15

Since the two parameters of function Change: first and second are passed by reference, when function call Change(num,num) is made, both first and second are aliases for the same variable num. Initially, num=8, after first += 2, num=8+2=10; after second *= 2, num =10*2=20. So the output will be 20.

When num is initialized to 3, the same thing happens, the result is (3+2)*2= 10.

6.17

 
void Swap( int &a, int &b )
{
  int t;
  t = a;
  a = b;
  b = t;
}