Need help to sort data and make class

[pangdo]

1. I have few data in "MyData.txt" :
9 7 4 4 6 5 9 1 3 4 7 6 5 4 1 4 8 6 4 8 5
I only can copy the data into the code like this :

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char **argv){
char ofilename[] = "Sort-MyData.txt";
ofstream fout;
fout.open(ofilename);

const int n = 21;
int x[n] = {9, 7, 4, 4, 6, 5, 9, 1, 3, 4, 7, 6, 5, 4, 1, 4, 8, 6, 4, 8, 5};

for(int i = 0; i < n; i++) {
cout << x[i] << " ";
}

cout << endl;
for(int i = 0; i < n-1; i++) {
for(int j = i+1; j < n; j++) {
if(x[i] > x[j]) {
int buf = x[j];
x[j] = x[i];
x[i] = buf;
}
}
}

for(int i = 0; i < n; i++) {
fout << x[i] << " ";
}

fout.close();
cout << endl;
system("pause");
}

And the result in "Sort-MyData.txt" :
1 1 3 4 4 4 4 4 4 5 5 5 6 6 6 7 7 8 8 9 9
So the code is true.
But if I "call" the input from the code :

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char **argv){
    //Input file
    char ifilename[] = "MyData.txt";
    ifstream fin;
    fin.open(ifilename);
    
    //Output file
    char ofilename[] = "Sort-MyData.txt";
    ofstream fout;
    fout.open(ofilename);
    
    //Check whether the ifilename exists
    if (!fin) {
              cerr << "Error!" << ifilename;
              cerr << "could not be opened" << endl;
              exit (1);
              }
    
    //Reading input file, I'm confused here :(
    int i;
    const int n = 21;
    int x[n];
    while (!fin.eof()) {
                           fin >> x[n];
                           i++;
                           }
    
    //Show the original data
    for (int i = 0; i < n; i++){
        cout << x[i] << " ";
        }
    
    //Sort the data
    for(int i = 0; i < n-1; i++) {
    for(int j = i+1; j < n; j++) {
            if(x[i] > x[j]) {
                    int buf = x[j];
                    x[j] = x[i];
                    x[i] = buf;
                    }
                    }
                    }
                    
    //Save output                
    for(int i = 0; i < n; i++) {
            fout << x[i] << " ";
            }
            
            fin.close();
            fout.close();
            system("pause");
            }

It shows strange number in "Sort-MyData.txt" :
-1 0 0 0 0 2 28 530 1088 1096 2292980 2293004 2293068 2503056 4198400 4198400 4198400 4198400 1977537193 2000486448 2000494924
I think there's something wrong in code for reading input file.
What should I do?

2. Then how to make 3 equal classes for "Sort-MyData.txt"?

3. If I have so many data in "MyData.txt",
(let say that there are thousands lines of data and there are hundreds data in each line),
what should I do?
(Because I don't know exactly how many data in "MyData.txt" and it is impossible to count it)

Thank you. :)

[jonsca]

i = 0;
while (fin >> x[i] ) 
{
       i++;
       if( i ==n)   //less than elegant but it's off by 1 if you && it in
            break; //to the loop condition
       
}

What you had was going out of bounds over and over --->fin >> x[n]; (n=20 is the last element of the array)

If you don't know how many data you will be reading in you are better off using a STL vector. They expand in capacity as the need arises.

Otherwise you could either get the total number of points from the user and use int * myarr = new int[numberuserentered]; Failing that you can set an upper limit MAX_SIZE and declare int arr[MAX_SIZE];

I don't quite understand what you are asking on the 2nd question.

[pangdo]

The 2nd problem means how to divide the data in "Sort-MyData.txt" into 3 groups :
1 1 3 4 4 4 4
4 4 5 5 5 6 6
6 7 7 8 8 9 9

I'm really sorry, I think I made a mistake in write the title of this thread because it is not class problem.

[jonsca]

Just into 3 groups, cutting off the count at 7? Just make 3 arrays that are 1/3 the size of the big array (if it doesn't divide evenly you'd have to make a 4th array) and copy the ints over element by element.