C++ Array Sum Values Around Coordinate

Question

I'm having some difficulty summing the values of a multidimensional array around the coordinates given below. Something is wrong with my logic with the index location. Any ideas would be very helpful and if more information is needed, please don't hesitate to ask me.

#include <iostream>
#include <ctime>


using namespace std;

int main()
{
srand(time(0));

int displayArray[11][11];

    cout<<"\t\t\t\t\t\t\t\t\t\t\t\t\tColumn\n\n";
    for(int column=1;column<10;column++)
    {
        cout<<"\t "<<column;
    }
    cout<<"\n\n";
    //fill array with random numbers

    for(int i=0;i<9;i++)
    {
        for(int m=0;m<9;m++)
        {
            displayArray[i][m]=rand()%10;
        }
    }

    cout<<"\n\n\n";

    //main data printout

    for(int k=0;k<9;k++)
    {
        cout<<"Row "<<k+1<<"\t ";

    for(int l=0;l<9;l++)
    {
        cout<<displayArray[k][l]<<"\t";
    }
    cout<<endl<<endl;
    }

    cout<<"\n\n";

    int row=0, column=0;
    cout<<"What array cell would you like to see? (Press enter after each entry)\n";
    cout<<"Row = ";
    cin>>row;
    cout<<"Column = ";
    cin>>column;
    cout<<"\nThe number "<<displayArray[row-1][column-1]<<" is in cell "<<row<<","<<column;

    int coord1=displayArray[row-2][column+2],
        coord2=displayArray[row+2][column+2],
        coord3=displayArray[row-2][column-2],
        coord4=displayArray[row-2][column+2],
        coord5=displayArray[row-2][column+2],
        coord6=displayArray[row-2][column+2],
        coord7=displayArray[row-2][column+2],
        coord8=displayArray[row-2][column+2];

    int sum=coord1+coord2+coord3+coord4+coord5+coord6+coord7+coord8;

    cout<<"\n\nThe sum of the cells surrounding "<<row<<","<<column<<" is "<<sum;

    cin.get();
    cin.get();


return 0;
}

What, exactly, is the problem?

Cody Gray
– Cody Gray ♦

2013-04-16 03:35:31 +00:00
Commented Apr 16, 2013 at 3:35 — Cody Gray
– Cody Gray ♦, Commented Apr 16, 2013 at 3:35

Southpaw Hare · Accepted Answer · 2013-04-16 03:48:26Z

1

Your problem may be that you are using row/column -2 and row/column +2 as your adjacent directions, which is not correct. If (row-1, col-1) is your current cell, than you want row/col -2 and row/col +0.

int coord1=displayArray[row-2][column-2],
    coord2=displayArray[row-2][column-1],
    coord3=displayArray[row-2][column],
    coord4=displayArray[row-1][column-2],
    coord5=displayArray[row-1][column],
    coord6=displayArray[row][column-2],
    coord7=displayArray[row][column-1],
    coord8=displayArray[row][column];
int sum=coord1+coord2+coord3+coord4+coord5+coord6+coord7+coord8;

This can be done much more programmatically, however:

int sum = 0;
for (int x=row-2; x<=row; x++) {
    for (int y=column-2; y<=column; y++) {
        if ((x != row-1) || (y != column-1)) { //Avoids "center" cell (self)
            sum += displayArray[x][y]
        }
    }
}

edited Apr 16, 2013 at 3:48

answered Apr 16, 2013 at 3:36

Southpaw Hare

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Comments

Alec · Accepted Answer · 2013-04-16 03:39:13Z

1

So if I'm understanding this correctly, the user inputs a row and column number, which corresponds to the value located in displayArray[row-1][column-1]

Thus, the coordinates around that cell should be.

displayArray[row][column]
displayArray[row-1][column]
displayArray[row-2][column]
displayArray[row][column-1]
displayArray[row-2][column-1]
displayArray[row][column-2]
displayArray[row-1][column-2]
displayArray[row-2][column-2]

I'm not sure exactly why you're using the coordinates you are, but that is your problem.

Also, you're going to want to make sure your program doesn't crash if the user selects a cell on the border of the array. eg: If you try to search coordinates around the cell (0,0), the program will crash when trying to load a value for displayArray[-1][-1]

answered Apr 16, 2013 at 3:39

Alec

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3 Comments

Klinetel Over a year ago

Thank you, how would you suggest preventing a crash?

Alec Over a year ago

The simplest way is with if statements. First declare all your coordinates to be equal to 0, and then use if statements before assigning them values. ex: if (column >= 2 && row >= 2) { //assign coordinate values} You would then need a few more if statements to catch if column was greater than 2, but not row, etc. Honestly, a code rework would be good (Southpaw Hare provides a good example), but you can do this too.

Alec Over a year ago

No problem! Good luck coding :)

Gabe Sechan · Accepted Answer · 2013-04-16 03:38:19Z

0

Your mistake is in translating 0 based to 1 based indexing. The arrays are 0 based. You're having them enter in a 1 based row. Then you want to add the 8 numbers around it. If they entered 0 based numbers and entered N, you'd want to sum [n-1], n, and n+1 for each row/column. To deal with 0 based, you want to do n-2, n-1, and n. But you're doing n-2 and n+2. You're also not calculating the middle of the rows anywhere near right.

Best practice is not even to do the math like that. It would be to read in the row/column number, then immediately subtract 1 to make it 0 based, and deal with it as 0 based from then on.

answered Apr 16, 2013 at 3:38

Gabe Sechan

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