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;
}

Answer 1

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-calculate the column sums so you won't need to repeat it.

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]