How to change the position of sectors in the matrix?-CodePudding

A task: Fill in the sectors of the matrix that lie to the left and right of the main and secondary diagonals, from the upper left corner to the right - down. Fill the rest of the matrix with zeros.

What happened to me:

#include <stdio.h> 
int main()
{ 
        int a[9][9], n=9, t=1, i, j;
        for(j=0; j<n; j  )
                for(i=0; i<n; i  )
                        if((j<i && i<n/2) || (j<n-i-1 && i>=n/2) || (j>n-i-1 && i<n/2) || (j>i && i>=n/2))
                                a[i][j]=t  ;
                        else
                                a[i][j]=0;
        for(i=0; i<n; i  )
        {
                for(j=0; j<n; j  )
                        printf("M", a[i][j]);
                printf("\n");
        }
        return 0;
}

CodePudding user response：

Your first pair of nested nested loops are inverted. The following

for(j=0; j<n; j  )
    for(i=0; i<n; i  )

should be

for(i=0; i<n; i  )
    for(j=0; j<n; j  )

Better code formatting and variable names help to spot errors like these.

Note that introducing a third control variable for the edge distance in each line helps to remove a lot of complexity from the conditional statement.

For example:

#include <stdio.h>

#define SIZE 9
#define GROWTH 1

int main(void)
{
    for (int row = 0, edge = 0, number = 1; row < SIZE; row  ) {
        for (int column = 0; column < SIZE; column  ) {
            printf("M", (column < edge || SIZE - column <= edge) ? number   : 0);
        }

        printf("\n");
        edge  = row < SIZE / 2 ? GROWTH : -GROWTH;
    }
}

Fixing the for loop order in your program, or using the example above, both produce this output:

   0   0   0   0   0   0   0   0   0
   1   0   0   0   0   0   0   0   2
   3   4   0   0   0   0   0   5   6
   7   8   9   0   0   0  10  11  12
  13  14  15  16   0  17  18  19  20
  21  22  23   0   0   0  24  25  26
  27  28   0   0   0   0   0  29  30
  31   0   0   0   0   0   0   0  32
   0   0   0   0   0   0   0   0   0