Read numbers from a file into a multidimensional array

Question

I have a .txt file that is formatted as follows:

906 25 25
1997 25 25
900 25 25
1990 50 1.75
1981 50 50
925 25 25

I have written the following code to read the numbers into an array:

float numbers[1029][2];
std::ifstream fin;
fin.open("GiftCardFinal.txt");
if (!fin.is_open())
{
    return 0;
}
for (int i = 0; i < 1029; i++)
{
    for (int j = 0; j < 3; j++)
    {
        fin >> numbers[i][j];
    }
    
}
fin.close();

However, when I run this code to test if it read the numbers correctly...

std::cout << numbers[0][0] << " ";
std::cout << numbers[0][1] << " ";
std::cout << numbers[0][2] << " ";
std::cout << std::endl << std::endl;
std::cout << numbers[1][0] << " ";
std::cout << numbers[1][1] << " ";
std::cout << numbers[1][2] << " ";

It outputs:

906 25 25

25 1997 25

Can anyone help with this or offer advice on what I can improve?

std::cout << numbers[0][2] goes outside the boundaries of the 2nd array dimension. — jkb
– jkb, Commented Feb 7, 2021 at 6:10
I did originally set it to 3. I changed it to 2 when I didn’t understand why it wasn’t working — ZachSal
– ZachSal, Commented Feb 7, 2021 at 6:14
Setting it to 3 results in the following output: 906 25 1997 1997 25 900 — ZachSal
– ZachSal, Commented Feb 7, 2021 at 6:16
When you set the 2nd dimension to 3, your inner loop is not filling the 2nd dimension. Try j < 3 — jkb
– jkb, Commented Feb 7, 2021 at 6:20

biqarboy · Accepted Answer · 2021-02-07 06:35:03Z

1

Try to run this code:

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

#define NUM_LINE 10000

int main()
{
    float numbers[NUM_LINE][3];
    std::ifstream fin;
    fin.open("GiftCardFinal.txt");
    if (!fin.is_open())
    {
        return 0;
    }
    for (int i = 0; i < NUM_LINE; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            fin >> numbers[i][j];
        }
        
    }
    fin.close();
    
    for (int i = 0; i < NUM_LINE; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            cout << numbers[i][j] << " ";
        }
        cout << endl;
    }

    return 0;
}

Output:

906 25 25
1997 25 25
900 25 25
1990 50 1.75
1981 50 50
925 25 25

edited Feb 7, 2021 at 6:35

answered Feb 7, 2021 at 6:23

biqarboy

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6 Comments

ZachSal Over a year ago

It has to read ~1000 rows and 3 columns each

biqarboy Over a year ago

I updated my code. You can change the value of NUM_LINE if you already know the number of lines in your input file. Check this post if you do not know the number of lines in the input file beforehand.

ZachSal Over a year ago

How are the for loops different from the original ones? Thank you for the help

biqarboy Over a year ago

I moved the point of code change to one line instead of three. Check your numbers array declaration and the outer for loops. Right now you need to only change the value of number of lines in #define NUM_LINE 10000.

biqarboy Over a year ago

Your code did not work because you declared the numbers array with wrong dimension. It should be 1029 x 3.

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