arrays.cpp

how to add arrays * Use of const (constant) values. * Creation of vectors. * Passing

/*

Sample Array Declaration and Use

File: ARRAYS.CPP
Version: 3.0
Created: 9/26/96
Last Updated: 10/20/99
Written by: Dr. C. S. Tritt

*/

#include <iostream> // Header for stream I/O
#include <fstream> // Header for file I/O
#include <iomanip> // Header for I/O stream manipulators
#include <vector> // Header for vector class

using namespace std;

// Declare function(s).

double asum(vector<double> const& vector_to_sum, int number_to_sum);

int main(void)
{
// Declare and initialize variables.

   const int MAX_SIZE = 10;  // The const modifier assures that size can't be changed.
   int size = 0;  // Actual size of the array (counting from zero).
   int count; // Loop counter (will be initialized in for loop).
   vector<double> a(MAX_SIZE);  // Declare the array to hold MAX_SIZE values.
   ifstream fin;  // Declare an input file stream.

// Open the input file and check for errors.

   fin.open("asum.in", ios::in);
   if (!fin)
   {
      cout << "Can't open input file\n";
      return 1;
   }

// Read array from a file and check for errors.

   while ((size < MAX_SIZE) && (fin >> a[size])) ++size; // Short circuit evaluation required.
   if (fin.fail() && !fin.eof())
   {
      cout << "Error while reading line " << size + 1 << ".  Aborting.\n";
      fin.close();
      return 1;
   }
   else if (size == MAX_SIZE) cout << "Array full.  Some data may be ignored.\n";

// Echo it.

   cout << showpoint << setprecision(3); // Set reasonable output format.
   cout << "After read A is: ";
   for (count = 0; count < size; ++count) cout << a[count] << " ";
   cout << endl;

// Call the asum function.

   cout << "The sum of its elements is: " << asum(a, size) << "\n";

// Create a second vector, initialize it with ones and display it.

   vector<double> spare(MAX_SIZE, 1.0);
   cout << "After creation spare is: ";
   for (count = 0; count < MAX_SIZE; ++count) cout << spare[count] << " ";
   cout << endl;

// Show sizes, resize and show sizes again.

   cout << "Size of vector a: " << a.size() << " and ";
   cout << "Size of vector spare: " << spare.size() << endl;
   a.resize(size);
   spare.resize(size);
   cout << "After resize to size:\n";
   cout << "Size of vector a: " << a.size() << " and ";
   cout << "Size of vector spare: " << spare.size() << endl;

// Remove element size/2 from a, insert it into spare and display results.

   int element = size / 2;
   spare.insert(spare.begin() + element, a[element]); // .begin() required to produce iterator type.
   a.erase(a.begin() + element); // .begin() required to produce iterator type.
   cout << "A: ";
   for (count = 0; count < size - 1; ++count) cout << a[count] << " ";
   cout << endl;
   cout << "Spare: ";
   for (count = 0; count < size + 1; ++count) cout << spare[count] << " ";
   cout << endl;

// Swap a and spare.

   a.swap(spare);
   cout << "After swap:\n";
   cout << "A: ";
   for (count = 0; count < size + 1; ++count) cout << a[count] << " ";
   cout << endl;
   cout << "Spare: ";
   for (count = 0; count < size - 1; ++count) cout << spare[count] << " ";
   cout << endl;

// Test empty on spare, clear it and try again.

   cout << "Before clear... ";
   cout << "spare.empty() = " << spare.empty() << " and ";
   cout << "size of spare = " << spare.size() << endl;
   spare.clear();
   cout << "After clear... ";
   cout << "spare.empty = " << spare.empty() <<" and ";
   cout << "size of spare = " << spare.size() << endl;

// Close file and return a zero if everything worked.

   fin.close();
   return 0;
}

// Define the function.

double asum(vector<double> const& a, int n)
{
// This function returns the sum of the first n (or all) values in array a.

   if (n >= a.size()) 
   {
      cout << "Requested size greater than array size, summing all elements.\n";
      n = a.size();

   }
   double sum = 0.0;  // This is the running sum.
   int count;  // This is the loop counter.

   for (count = 0; count < n; ++count) sum = sum + a[count];

   return sum;
}