CODEWITHSUNDEEP
c++arraystext-files
Rey H
Rey H

Reputation: 3

Read a text file of numbers and store into an array of integers in C++

I need to store an array of integers from a text file, but I can't find what I need to do for it exactly. I think I have the basis of the code set up, but I think I need to convert the elements into integers or something?

My output is my list :

50 0 20 10 18 -5 15 22 34 -1

But my "sorted" list ends up being -1, and a series of large negative numbers. I troubleshooted it to being something wrong with the array.

#include <iostream>
#include <fstream>
using namespace std;
int main() 
{
    int array1[30];
    int counter=0,n=0;
    fstream datafile;
    void bubbleSort(int list[], int length);
    void selectionSort(int list[], int length);
    /////////////
    datafile.open("data.txt");
    if (!datafile.is_open())
    {
        cout << "Failure to open." << endl;
        return 0;
    }
    while (!datafile.eof()) {
        datafile >> array1[counter];
        n++;
        cout << array1[counter] << endl;
    }
    datafile.close();
    //////////////////////////////
    //bubbleSort(array1, n);
    //selectionSort(array1, n);
    for (int i = 0; i < n; i++)
        cout << array1[i] << ", ";

    system("pause");
    return 0;
}

Upvotes: 0

Views: 1001

Answers (2)

Ani Menon
Ani Menon

Reputation: 28199

Your code is all good except :

 while (!datafile.eof()) {
        datafile >> array1[counter];
        n++;
        cout << array1[counter] << endl;
    }

It should be:

while (!datafile.eof()) {
        datafile >> array1[n];
        if ( datafile.fail() ) break; 
        cout << array1[n] << endl;
        n++;
    }

Only a single index variable(n) is required to parse/store into a 1D array. The increment statement n++ in a while should always be the last one so that you are working on the current element and not the next.

Code:

#include <iostream>
#include <fstream>
using namespace std;
int main() 
{
    int array1[30];
    int n=0;
    fstream datafile;
    void bubbleSort(int list[], int length);
    void selectionSort(int list[], int length);
    /////////////
    datafile.open("data.txt");
    if (!datafile.is_open())
    {
        cout << "Failure to open." << endl;
        return 0;
    }
    while (!datafile.eof()) {
        datafile >> array1[n];
        if (datafile.fail()) break;
        cout << array1[n] << endl;
        n++;
    }
    datafile.close();
    for (int i = 0; i < n; i++)
        cout << array1[i] << ", ";

    system("pause");
    return 0;
}

Upvotes: 0

Roland Illig
Roland Illig

Reputation: 41617

Never use eof(), since it leads to wrong programs. See https://stackoverflow.com/a/5837670 for the reason.

while (n < 30 && datafile >> array1[n]) {
    cout << array1[n] << endl;
    n++;
}
{
    int excess;
    if (datafile >> excess) {
        cerr << "error: data file too large\n";
        return;
    }
}

That way, the n will be correct at the end of the program.

Upvotes: 1

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