C++ Input/output

Question

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    int a , b , c , i , n;
    int d = 0;
 ifstream myfile;
 myfile.open("Duomenys1.txt");
 myfile >> n;
 for (int i = 0; i < n; i++ )
 {
     myfile >> a >> b >> c;
     d +=  (a + b + c)/3 ;
 }
ofstream myotherfile;
myotherfile.open ("Rezultatai1.txt");
myotherfile << d;
myotherfile.close();
myotherfile.close();
return 0;
}

The programs should read 3 (3 is n) rows of numbers (5 7 4 ; 9 9 8; 8 7 8), rows are summed up separately and given 3 different averages (7 ; 9 ; 8) in the Rezultatai1.txt file. But I only get -2143899376 result.

The problem isn't the huge number, I need the program to give every row's average number separately in the output file, so that in the output file its written (7 ; 9 ; 8)

Is the program you show the actual program you run? Is the data you show for the input file the actual data? Then you should get 20 as result in the output file. — Some programmer dude
– Some programmer dude, Commented Jul 18, 2015 at 8:46
works fine for me (result is 5+8+7=20). How does your input file look like? Btw, integer arithmetic gives (9+9+8)/3=8 not 9. — Walter
– Walter, Commented Jul 18, 2015 at 8:46
@Walter I just used the number the OP provided as the averages, though they are wrong. — Some programmer dude
– Some programmer dude, Commented Jul 18, 2015 at 8:48
@ParanoidParrot There's no rounding in your program, you use only integer arithmetic so the results are truncated. — Some programmer dude
– Some programmer dude, Commented Jul 18, 2015 at 8:55

Walter · Accepted Answer · 2015-07-18 09:10:29Z

1

You must make one output per line and you must use floating point arithmetic followed by rounding if you want rounded averages.

#include <iostream>
#include <iostream>
#include <cmath>

int main()
{
  const int numbers_per_lines = 3;
  std::ofstream output("Rezultatai1.txt");
  std::ifstream input("Duomenys1.txt");
  int number_of_lines;
  input >> number_of_lines;
  for(int i=0; i<number_of_lines; ++i) {
    double sum=0;
    for(int num=0; num<numbers_per_line; ++num) {
      double x;
      input >> x;
      sum += x;
    }
    output << i << ' ' << std::round(sum/numbers_per_line) << std::endl;
  }
}

answered Jul 18, 2015 at 9:10

Walter

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Comments

Some programmer dude · Accepted Answer · 2015-07-18 09:11:27Z

1

Two problems: First of all you don't do any rounding, instead since you use integer arithmetic the result is truncated. There are a couple of ways to do rounding, one of the simple is to use floating point arithmetic, and use e.g. std::round (or std::lround) to round to nearest integer value. Like e.g.

d = std::round((a + b + c) / 3.0);

Notice the use of the floating point literal 3.0 when dividing.

The second problem is that you don't write the averages, you sum all averages and write the sum. This can be fixed by simple write the average in the loop instead of after the loop, and use plain assignment instead of increase-and-assign.

answered Jul 18, 2015 at 9:11

Some programmer dude

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Comments

Shreevardhan · Accepted Answer · 2015-07-18 10:53:09Z

0

I'd suggest this

#include <iostream>
#include <cstdio>
using namespace std;

int main() {
    freopen("Duomenys1.txt", "r", stdin);    // Reopen stream with different file
    freopen("Rezultatai1.txt", "w", stdout);
    int n, a, b, c;
    cin >> n;
    while (n--) {
        cin >> a >> b >> c;
        cout << (a + b + c) / 3 << endl;
    }
    return 0;
}

Input

Output

5
8
7

See DEMO.

answered Jul 18, 2015 at 10:53

Shreevardhan

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