Summarize then average every 10 lines from a txt file

Question

I have this code for the task mentioned in the title:

The program reads from a 1 columned text file in which the numbers are below each other.

#include <iostream>
#include <fstream>

using namespace std;

int main()
{

    double number;
    double sum = 0;

    ifstream average;
    average.open("average.txt");

    while (average >> number)
    {
        for(int i = 0; i < 10; i++)
        {
            sum = sum + number;

            i++;

            if (i = 9)
            {
                cout << sum / 10 << endl;
            }
         }
    {

    average.close();
    system("pause");
    return 0;
}

But somehow it doesn't average the numbers just divide all of them by 10.

What might be the problem?

Thanks

Time to learn [how to debug small programs](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/). — StoryTeller - Unslander Monica, Aug 23 '17 at 13:30
The order of `while` and `for` seems wrong. You are reading 1 number and using that 10 times in the for loop. — ikkuh, Aug 23 '17 at 13:31
As I know the `while (average >> number)` is the same as `while (!average.eof())`...`getline` — introvertbustardxd, Aug 23 '17 at 13:37
`if (i = 9)` is assignment, not comparison. It's also always true. ` i++;` inside the loop and inside the `for` means you increment it twice per iteration. — Retired Ninja, Aug 23 '17 at 13:38

petrpulc · Accepted Answer · 2017-08-23T14:49:12.287

1

A possible solution:

int i;
while (average.good()) // only while we are good
{
  sum = 0; // you need to clean it
  for(i = 0; i < 10; i++)
  {   
    average >> number;

    if (!average.good()) break; // if number of lines is not mod10

    sum = sum + number;
    // i++; you already do that in for loop
  }
  if (i)
  {
    cout << sum / i << endl; // only print after each 10 or less
  }
}

Or with the single loop:

sum = 0;
int i = 0;

while (average >> number) {
  sum = sum + number;
  ++i;

  if (i == 10) {
    cout << sum / i << endl;
    sum = i = 0;
  }
}
if (i) {
  cout << sum / i << endl;
}

edited Aug 23 '17 at 14:49

answered Aug 23 '17 at 13:43

petrpulc

940
6
22

https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-considered-wrong – Retired Ninja Aug 23 '17 at 13:44
@RetiredNinja typing faster than thinking, of course – petrpulc Aug 23 '17 at 13:47

score 0 · Answer 2 · answered Aug 23 '17 at 14:33

You could achieve this easily with a std::deque since you can easily add and remove numbers when you reach the tenth quota every line.

#include <fstream>
#include <deque>
#include <numeric>

int main()
{
    std::ifstream read("average.txt");

    constexpr unsigned linesToAverage = 10;
    std::deque<double> numbers;
    double currentNumber = 0.0;

    while (read >> currentNumber) {
        if (numbers.size() == linesToAverage) {
            std::cout << std::accumulate(std::begin(numbers), std::end(numbers), 0.0) / linesToAverage << std::endl;
            numbers.pop_back();
        }

        numbers.push_front(currentNumber);
    }

    return 0;
}

This code shows the averages starting from the first ten numbers.

Summarize then average every 10 lines from a txt file

2 Answers2