Adding elements to a 2 dimensional array C++

Question

I’m writing this code where I fill a 2 dimensional array with information from a file. Here’s the file:

5 

Franks,Tom 2 3 8 3 6 3 5 

Gates,Bill 8 8 3 0 8 2 0 

Jordan,Michael 9 10 4 7 0 0 0 

Bush,George  5 6 5 6 5 6 5 

Heinke,Lonnie  7 3 8 7 2 5 7

Now the numbers are going in the array: data[50][8].

I also total all the numbers in each line which I have done. I want to add this total to the data array so it looks something like 2 3 8 3 6 5 3 30. How do I do this? Here’s all my code if you wanted to see it:

int main()
{

    ifstream fin;
    char ch;
    int data[50][8];
    string names[50];

    fin.open("empdata.txt");

    int sum = 0;
    int numOfNames;
    fin >> numOfNames;

    for (int i = 0; i < numOfNames; i++) {

        fin >> names[i];

        for (int j = 0; j < 7; j++) {
            fin >> data[i][j];
        }
            }

        for (int i = 0; i < 5; i++)
        {

            for (int j = 0; j < 7; j++)
            {
                sum += data[i][j];

            }
            cout << sum << endl;
            sum = 0;
        }
}

Here's the new code that c650 helped me with. It's not outputting anything now: int main() {

ifstream fin;
char ch;
int data[50][8];
string names[50];

fin.open("empdata.txt");

int sum = 0;
int numOfNames;
fin >> numOfNames;

for (int i = 0; i < numOfNames; i++) {

    fin >> names[i];

    data[i][7] = 0;

    for (int j = 0; j < 7; j++) {
        fin >> data[i][j];
        data[i][7] += data[i][j];
    }
}

for (int i = 0; i < numOfNames; i++)
{
    cout << data[i][7] << endl;

}



system("pause");
return 0;

}

I'd recommend you use the STL. A std::vector may really help you out! — Charles
– Charles, Commented Nov 1, 2016 at 23:37

Charles · Accepted Answer · 2016-11-02 00:12:09Z

1

The following seems like what you are trying to do. I will point the flaws in the code you've presented.

This is not the best way to do it, but according to OP there are some constraints, such as not being able to use the STL.

/*  1 */  #include <fstream>
/*  2 */  #include <iostream>
/*  3 */  #include <string>
/*  4 */  
/*  5 */  using namespace std;
/*  6 */  int main()
/*  7 */  {
/*  8 */  
/*  9 */      ifstream fin;
/* 10 */      int data[50][8];
/* 11 */      string names[50];
/* 12 */  
/* 13 */      fin.open("test.txt");
/* 14 */  
/* 15 */      int numOfNames;
/* 16 */      fin >> numOfNames;
/* 17 */  
/* 18 */      for (int i = 0; i < numOfNames; i++) {
/* 19 */  
/* 20 */          fin >> names[i];
/* 21 */  
/* 22 */          data[i][7] = 0; /* use last spot in array for sum, set to 0. */
/* 23 */          for (int j = 0; j < 7; j++) {
/* 24 */              fin >> data[i][j];
/* 25 */              data[i][7] += data[i][j];
/* 26 */          }
/* 27 */      }
/* 28 */  
/* 29 */      for (int i = 0; i < numOfNames; i++)
/* 30 */      {
/* 31 */          cout << data[i][7] << endl; /* add each element to the sum here*/
/* 32 */      }
/* 33 */      return 0;
/* 34 */  }

OP was having a problem where no output was generated. OP, you must make sure that the your input file has the correct name...

edited Nov 2, 2016 at 0:12

answered Nov 1, 2016 at 23:49

Charles

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9 Comments

Ralf Over a year ago

Ok that seems like it would work but it's not outputting anything now. Here's the code

Ralf Over a year ago

data[i][7] += data[i][j]; } } for (int i = 0; i < numOfNames; i++) { cout << data[i][7] << endl; } system("pause"); return 0; }

Ralf Over a year ago

ohhh that didn't past right, hold up I'll just edit my top question

Charles Over a year ago

@Ralf: I am afraid that I cannot reproduce your "no output" results. Are you sure your input file is named correctly?

Ralf Over a year ago

Oh yeah...that was my problem. It works now! Thanks so much for your help :)

|

Thomas Matthews · Accepted Answer · 2016-11-01 23:55:17Z

0

As I've answered in other similar posts: Use a structure to model the record.

struct Record
{
  std::string last_name;
  std::string first_name;
  unsigned int grades[MAXIMUM_GRADES];
};

This allows you to have an array of mixed types:

Record student_info[MAXIMUM_STUDENTS];

To make reading from a file easier, you can overload operator>> inside the structure:

struct Record
{
  //...
  friend std::istream& operator>>(std::istream& input, Record& r);
};

std::istream& operator>>(std::istream& input, Record r)
{
  std::getline(input, r.last_name, ',');
  std::getline(input, r.first_name, ' ');
  for (unsigned int i = 0; i < MAXIMUM_GRADES; ++i)
  {
    input >> r.grades[i];
  }
  return input;
}

This simplifies your input loop:

for (unsigned int i = 0; i < MAXIMUM_STUDENTS; ++i)
{
  my_data_file >> student_info[i];
}

Too bad you can't use std::vector. The std::vector is ideal for reading from files especially when you don't know the size of the file.

answered Nov 1, 2016 at 23:55

Thomas Matthews

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2 Comments

Real73 Over a year ago

this guy still don't about matrix how he could understand the struct ?

Thomas Matthews Over a year ago

@ShahrairNazimReal: Depends on the instruction course and the order of the topics discussed. There is no need to discuss arrays before structures. Structures can be discussed before arrays.

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