Question

4.4 Lab: Arrays of Pointers to Structures (Sort)

C++ programming

This assignment is based on Homework 3. The program will create an array of Airport structures. On the first line in the input file airports.txt there is an integer n, representing the number of lines in the input file. On each of the following n lines there is an airport code (a unique identifier) followed by the airport’s number of enplanements (commercial passenger boardings), and city served. You may assume that the data in the input file are sorted by the airport’s code as shown below:

4
BFL 100433 Bakersfield 
BUR 2077892 Burbank
LAX 39636042 Los Angeles 
MRY 192136 Monterey

Read n from this input file and use it to dynamically allocate an array of structures. Then continue reading from file to put data into the dynamically allocated array.

Create an array of n pointers to Airport structures and initialize each pointer to point to the corresponding element in the array of Airport structures.

Change the insertion sort algorithm to rearrange the pointes in the array of pointers to show the array of structures in descending order by the airport’s number of enplanements.

When done sorting the pointers, display the following report:

Original Order                   Descending (enp)
BFL Bakersfield        100433    LAX Los Angeles      39636042
BUR Burbank           2077892    BUR Burbank           2077892
LAX Los Angeles      39636042    MRY Monterey           192136
MRY Monterey           192136    BFL Bakersfield        100433

/*~*~*~*~*~*~
Pointers, Arrays, Structures, Sorting, and Dynamic Allocation of Memory
Name:
IDE:
*/

#include <iostream>
#include <string>
#include <fstream>
#include <iomanip>

using namespace std;

struct Airport
{
string code;
string city;
int enp;
};

// function prototypes
Airport *readArpData(string filename, int &size);
Airport **createPtrArray(Airport *list, int size);
void insertSort(Airport **pArp, int size);
void displayReport(Airport **pArp, Airport *list, int size);

int main()
{
Airport *list; // pointer to work with a dynamically allocated array of structs
Airport **pArp; // pointer to work with an array of pointers to structs
int size;
string filename = "airports.txt";
  
// function calls
cout << "Enter input file name: ";
cin >> filename;
// call readArpData
// call createPtrArray
// call insertSort
// call displayReport
  
return 0;
}

/*~*~*~*~*~*~
This function does the following:
- opens the input file(with validation: exit if file not found)
- reads size from the input file (the first number)
- dynamically allocates an array of size Airport structures
- reads data for size airports into the dynamically allocated array
- closes the input file
- returns the pointer to the dynamically allocated array
*~*/
Airport *readArpData(string filename, int &size)
{
ifstream inputFile;
Airport *list;
  
/* Write your code here */
  
return list;
}

/*~*~*~*~*~*~
This function ...

*~*/
Airport **createPtrArray(Airport *list, int size)
{
Airport **pArp;
  
/* Write your code here */
  
return pArp;
}

/*~*~*~*~*~*~
This function ...

*~*/
void insertSort(Airport **list, int size)
{
/* Write your code here */
}

/*~*~*~*~*~*~
This function ...

*~*/
void displayReport(Airport **pArp, Airport *list, int size)
{
cout << "\nOriginal Data Descending (enp)" << endl;
for (int i = 0; i < size; i++){
cout << /* code */ << " "
<< setw(15) << left << /* city */
<< setw(10) << right << /* enp */ << " ";
cout << /* code */ << " "
<< setw(15) << left << /* city */
<< setw(10) << right << /* enp */ << endl;
}
}

/*~*~*~*~*~*~ Save the output below

*~*/

Answer 1

#include <iostream>
#include <string>
#include <fstream>
#include <iomanip>

using namespace std;

struct Airport
{
   string code;
   string city;
   int enp;
};

// function prototypes
Airport *readArpData(string filename, int &size);
Airport **createPtrArray(Airport *list, int size);
void insertSort(Airport **pArp, int size);
void displayReport(Airport **pArp, Airport *list, int size);

int main()
{
   Airport *list; // pointer to work with a dynamically allocated array of structs
   Airport **pArp; // pointer to work with an array of pointers to structs
   int size;
   string filename = "airports.txt";
  
   // function calls
   cout << "Enter input file name: ";
   cin >> filename;
   list = readArpData(filename,size);
   pArp = createPtrArray(list,size);
   insertSort(pArp,size);
   displayReport(pArp,list,size);

   return 0;
}

/*~*~*~*~*~*~
This function does the following:
- opens the input file(with validation: exit if file not found)
- reads size from the input file (the first number)
- dynamically allocates an array of size Airport structures
- reads data for size airports into the dynamically allocated array
- closes the input file
- returns the pointer to the dynamically allocated array
*~*/
Airport *readArpData(string filename, int &size)
{
   ifstream inputFile;
   Airport *list;
   inputFile.open(filename.c_str(),ios::in) ;
   if(inputFile==NULL)
   {
       cout<<"Error Opening File!!";
       return NULL;
   }
   inputFile>>size;
   /* Write your code here */
   list = new Airport[size];
   for(int i=0;i<size;i++)
   {
       inputFile>>list[i].code;
       inputFile>>list[i].enp;
       std::getline (inputFile,list[i].city);
   }
   inputFile.close();
   return list;
}

/*~*~*~*~*~*~
This function ...

*~*/
Airport **createPtrArray(Airport *list, int size)
{
   Airport **pArp;
   pArp = new Airport*[size];
   for(int i=0;i<size;i++)
   {
       pArp[i] = &list[i];
   }

return pArp;
}

/*~*~*~*~*~*~
This function ...

*~*/
void insertSort(Airport **list, int size)
{
   int i, j;
   Airport *key ;
    for (i = 1; i < size; i++)
    {
        key = (list[i]);
        j = i - 1;

        /* Move elements of arr[0..i-1], that are
        greater than key, to one position ahead
        of their current position */
        while (j >= 0 && list[j]->enp < key->enp)
        {
           list[j + 1] = list[j];
            j = j - 1;
        }
        list[j + 1] = key;
    }
}

/*~*~*~*~*~*~
This function ...

*~*/
void displayReport(Airport **pArp, Airport *list, int size)
{
cout << "\nOriginal Data Descending (enp)" << endl;
   for (int i = 0; i < size; i++){
       cout << list[i].code<< " "
       << setw(15) << left << list[i].city
       << setw(10) << right << list[i].enp << " ";
       cout << pArp[i]->code << " "
       << setw(15) << left << pArp[i]->city
       << setw(10) << right << pArp[i]->enp << endl;
   }
}

/*~*~*~*~*~*~ Save the output below

*~*/

//Output