Check if sums of i-th row and i-th column are same in 2d array

Question

I need to check if sums of i-th row and j-th column are same in 2d array and output i of the row and j of the column and sum. Also how can I make count it normally like [1][1],[1][2] etc.

Thanks in advance.

That's what I've got and sadly it's not working

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

int main()
{
    int sum1 = 0, sum2 = 0;
    int a[2][3];
    int i, j;

  for (i = 0; i<2; i++)
  {
    for (j = 0; j<3; j++)
    {
      printf("a[%d][%d] = ", i, j);
      scanf("%d", &a[i][j]);
    }
  }

  for (i = 0; i<2; i++)
  {
    sum1 = 0, sum2 = 0;
    for (j = 0; j<3; j++)
    {
     sum1 += a[i][j];
     sum2 += a[j][i];
    }
    if (sum1 == sum2)
        printf("row is %d and column is %d = %d", i, j, sum1);
  }


  return 0;
}

Please elaborate "it's not working". What is the output? What output in contrast do you expect? Why? Does it crash? Hang? Bluescreen? Endless loop? What exactly makes you think that something does not work? Did you debug? https://ericlippert.com/2014/03/05/how-to-debug-small-programs/ — Yunnosch, Mar 03 '20 at 18:49
Note that `sum1 += a[i][j]; sum2 += a[j][i];` will break the array bounds, the array is not square. — Weather Vane, Mar 03 '20 at 18:53
It is unclear what you mean by *"how can I make count it normally like `[1][1],[1][2]` etc."* Are you asking how to index arrays from `[1]`? — Weather Vane, Mar 03 '20 at 18:57

Support Ukraine · Accepted Answer · 2020-03-03T19:26:14.193

Your calculation of row sum seems correct but your calculation of column sum is wrong.

Try like:

  for (i = 0; i<2; i++)  // For every row
  {
    // Calculate row sum
    sumRow = 0;
    for (j = 0; j<3; j++)
    {
      sumRow += a[i][j];
    }

    for (j = 0; j<3; j++) // For every column
    {
      // Calculate column sum
      sumColumn = 0;
      for (i = 0; i<2; i++)
      {
        sumColumn += a[i][j];
      }

      // Compare results
      if (sumRow == sumColumn)
        printf("row is %d and column is %d = %d", i, j, sumRow);
    }
  }

The above code is however not efficient. A better way would be to pre-calculte the column sums so you wont need to do it again and again.

Something like:

  int columnSum[3] = {0};
  for (j = 0; j<3; j++) // For every column
  {
    // Calculate column sum
    for (i = 0; i<2; i++)
    {
      columnSum[j] += a[i][j];
    }
  }

  for (i = 0; i<2; i++)  // For every row
  {
    // Calculate row sum
    sumRow = 0;
    for (j = 0; j<3; j++)
    {
      sumRow += a[i][j];
    }

    for (j = 0; j<3; j++) // For every column
    {
      // Compare results
      if (sumRow == columnSum[j])
        printf("row is %d and column is %d = %d", i, j, sumRow);
    }
  }

Also how can I make count it normally like [1][1],[1][2]

If you want to program in C, you'll have to count like the language makes it natural - for instance start from zero. And further in row-major. So use

          Column 0  Column 1  Column 2

Row 0:    [0][0]    [0][1]    [0][2]

Row 1:    [1][0]    [1][1]    [1][2]

Check if sums of i-th row and i-th column are same in 2d array

1 Answers1