Adding/averaging numbers from a text file

[greenway]

I am really new to programming and this is probably something really simple but I have not found any videos or info on how to do it. I am trying to get specific positions from a file and add/average the numbers.

This is the text file(I will use [n] as line position, not as part of the file):

2016 116 303.1 Passengers 
2014 169 677.5 Interstellar 
2015 141 630.2 The Martian 
2013 91 723.2 Gravity 
2016 116 203.4 Arrival

For example, how would I get just 116 or 169, to add them together? I have to use their positions because the numbers themselves will be different but the format of the txt file will be the same.

[keskiverto]

It does look line that each line contains

int int double text

I would read each line into a string with getline.
Then, I would create istringstream from that string,
read int, int, double with formatted input and text with getline
from that istringstream object.
http://www.cplusplus.com/reference/sstream/istringstream/

[Ganado]

If the format of each line is {int} {int} {double} {string with one or more words}, parsing it isn't too bad.

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

int main()
{
	ifstream fin("movies.txt");
	
	int year;
	int number; // choose a better name, I'm just guessing as to what it means
	double rating; // choose a better name, I'm just guessing as to what it means
	while (fin >> year >> number >> rating)
	{
		string name;
		if (getline(fin >> ws, name))
		{
			cout << "Movie Year:   " << year << '\n'
			     << "Movie number: " << number << '\n'
			     << "Movie rating: " << rating << '\n'
			     << "Movie name:   " << name << "\n\n";
		}
	}
}

Input (movies.txt):

2016 116 303.1 Passengers
2014 169 677.5 Interstellar
2015 141 630.2 The Martian
2013 91 723.2 Gravity
2016 116 203.4 Arrival

Output:

Movie Year:   2016
Movie number: 116
Movie rating: 303.1
Movie name:   Passengers

Movie Year:   2014
Movie number: 169
Movie rating: 677.5
Movie name:   Interstellar

Movie Year:   2015
Movie number: 141
Movie rating: 630.2
Movie name:   The Martian

Movie Year:   2013
Movie number: 91
Movie rating: 723.2
Movie name:   Gravity

Movie Year:   2016
Movie number: 116
Movie rating: 203.4
Movie name:   Arrival

Note, the "fin >> ws" line filters out any whitespace before the getline call itself.
>> is delimited by whitespace, but getline can retain whitespace (in case the movie title is multiple words).

A file needs to be parsed. There's no way of magically jumping to the line that contains the number 169. You need to figure it out and check. A file is just characters/bytes.

Since the parsing here is relatively simple, I don't think you need to use stringstreams.

If you want to average them, then keep a variable for total number, and another variable for the number of movies, and then at the end, divide the total number by the number of movies.

[lastchance]

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
using namespace std;

//==========================================================

struct Movie
{
   int year;
   int minutes;
   double data;
   string name;
};

istream &operator >> ( istream &in, Movie &movie )
{
   in >> movie.year >> movie.minutes >> movie.data;
   getline( in >> ws, movie.name );
   return in;
}

//==========================================================

int main()
{
// ifstream in( "movies.txt" );
   istringstream in( "2016 116 303.1 Passengers\n"
                     "2014 169 677.5 Interstellar\n"
                     "2015 141 630.2 The Martian\n"
                     "2013 91 723.2 Gravity\n"
                     "2016 116 203.4 Arrival\n"     );

   vector<Movie> films;
   for ( Movie movie; in >> movie; films.push_back( movie ) );

   int sum = 0;
   for ( Movie &movie : films ) sum += movie.minutes;
   cout << "Sum = " << sum << '\n';
   cout << "Average = " << (double)sum / films.size() << '\n';
}

Sum = 633
Average = 126.6

If you aren't interested in storing all movie data, then you can find sums and averages of one column with much less:

#include <iostream>
#include <fstream>
#include <sstream>
using namespace std;

int main()
{
// ifstream in( "movies.txt" );
   istringstream in( "2016 116 303.1 Passengers\n"
                     "2014 169 677.5 Interstellar\n"
                     "2015 141 630.2 The Martian\n"
                     "2013 91 723.2 Gravity\n"
                     "2016 116 203.4 Arrival\n"     );
                     
   string dummy;
   int sum = 0, num = 0;
   for ( int value; in >> dummy >> value && getline( in, dummy ); num++ ) sum += value;
   cout << "Sum = " << sum << '\n';
   cout << "Average = " << (double)sum / num << '\n';
}

Sum = 633
Average = 126.6