Question

My attempts to find a way to get the average of this array have so far been fruitless. Any help would be appreciated.

#include <iostream>
#include <algorithm>
#include <numeric>
#include <vector>
#include <iterator>
#include <string>
#include <iostream>
#include <fstream>
using namespace std;
int main( )
{
    const int MAX = 100;
    double voltages[MAX];
    double average;
    ifstream thefile("c:\\voltages.txt");
        if(!thefile) 
    {
                cout<<"Error opening file"<<endl;
                system("pause");
                exit(1);
    }
        for(int count = 0; count < MAX; count++)
    {
                thefile >> voltages[count];
                cout << voltages[count++] << endl;
                average = voltages[count++]/count;
        if(count == 0 || thefile.eof())
    {
                break;
    }
    }
    cout << average;
    cout << "\n";
    system("PAUSE");
    return 0;
} 

voltages file is

100.8

120.4

121.4

111.9

123.4

but can have up to 100 doubles.

Answer 1

To calculate the average of the numbers stored in any C++ container (even raw arrays), use the following approach. Take the sum and divide by the number of elements:

std::accumulate(std::begin(v), std::end(v), 0.0) / (std::end(v) - std::begin(v));

Example code in action:

With std::vector /
With raw array (Note that only the definition of the vector / array changes!)

This code doesn’t check for zero length, which produces a division by zero. This will return a NaN value. This case can be detected in advance by using if (std::begin(v) == std::end(v)). You can handle such corner cases depending on your need if you don’t want to return NaN:

• Return a well-defined value such as 0.0
• Throw an exception
• Print a warning and exit (essentially the same as exception but can’t be caught)
• Custom error handling, for example set a boolean error variable to true