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// FILE: dynademo.cxx
// This is a small demonstration program showing how a dynamic array is used.
#include <iostream> // Provides cout and cin
#include <cstdlib> // Provides EXIT_SUCCESS and size_t
#include <cassert> // Provides assert
using namespace std;
// PROTOTYPES for functions used by this demonstration program
void allocate_doubles(double*& p, size_t& n);
// Postcondition: The user has been prompted for a size n, and this size has been read.
// The pointer p has been set to point to a new dynamic array containing n doubles.
// NOTE: If there is insufficient dynamic memory, then bad_alloc is thrown.
void fill_array(double data[ ], size_t n);
// Precondition: data is an array with at least n components.
// Postcondition: The user has been prompted to type n doubles, and these
// numbers have been read and placed in the first n components of the array.
double average(const double data[ ], size_t n);
// Precondition: data is an array with at least n components, and n > 0.
// Postcondition: The value returned is the average of data[0]..data[n-1].
void compare(const double data[ ], size_t n, double value);
// Precondition: data is an array with at least n components.
// Postcondition: The values data[0]..data[n-1] have been printed with a
// message saying whether they are above, below, or equal to value.
int main( )
{
double *numbers; // Will point to the first component of an array
size_t array_size;
double mean_value;
// Allocate an array of doubles to hold the user�s input.
cout << "This program will compute the average of some numbers. The\n";
cout << "numbers will be stored in an array of doubles that I allocate.\n";
allocate_doubles(numbers, array_size);
// Read the user�s input and compute the average.
fill_array(numbers, array_size);
mean_value = average(numbers, array_size);
// Print the output.
cout << "The average is: " << mean_value << endl;
compare(numbers, array_size, mean_value);
cout << "This was a mean program.";
return EXIT_SUCCESS;
}
void allocate_doubles(double*& p, size_t& n)
// Library facilities used: iostream.h, stdlib.h
{
cout << "How many doubles should I allocate?" << endl;
cout << "Please type a positive integer answer: ";
cin >> n;
p = new double[n];
}
void fill_array(double data[ ], size_t n)
// Library facilities used: cstdlib
{
size_t i;
cout << "Please type " << n << " double numbers: " << endl;
// Read the n numbers one at a time.
for (i = 0; i < n; ++i)
cin >> data[i];
}
void compare(const double data[ ], size_t n, double value)
{
size_t i;
for (i = 0; i < n; ++i)
{
cout << data[i];
if (data[i] < value)
cout << " is less than ";
else if (data[i] > value)
cout << " is more than ";
else
cout << " is equal to ";
cout << value << endl;
}
}
double average(const double data[ ], size_t n)
// Library facilities used: cassert, cstdlib
{
size_t i; // An array index
double sum; // The sum of data[0] through data[n - 1]
assert(n > 0);
// Add up the n numbers and return the average.
sum = 0;
for (i = 0; i < n; ++i)
sum += data[i];
return (sum/n);
}
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