how to set column to straight down like this?

Question

I tried to do a numeric puzzle and I want a column to set of like this

\ ----- ----- ----- -----
|  10 |  1  |  6  |  7  |
\ ----- ----- ----- -----
|  4  |  14 |  3  |  9  |
\ ----- ----- ----- -----
|  2  |  11 |  5  |     |
\ ----- ----- ----- -----
|  15 |  8  |  12 |  13 |
\ ----- ----- ----- -----

I tried to do this by using this code

    printf("\\ ----- ----- ----- -----\n");
    printf("|  %2.1d |  %2.1d |  %2.1d |  %2.1d |\n",a[0][0],a[0][1],a[0][2],a[0][3]);
    printf("\\ ----- ----- ----- -----\n");
    printf("|  %2.1d |  %2.1d |  %2.1d |  %2.1d |\n",a[1][0],a[1][1],a[1][2],a[1][3]);
    printf("\\ ----- ----- ----- -----\n");
    printf("|  %2.1d |  %2.1d |  %2.1d |  %2.1d |\n",a[2][0],a[2][1],a[2][2],a[2][3]);
    printf("\\ ----- ----- ----- -----\n");
    printf("|  %2.1d |  %2.1d |  %2.1d |  %2.1d |\n",a[3][0],a[3][1],a[3][2],a[3][3]);
    printf("\\ ----- ----- ----- -----");

It turn out to be like this

\ ----- ----- ----- -----
|   6 |  14 |  13 |  10 |
\ ----- ----- ----- -----
|   3 |   0 |   4 |   9 |
\ ----- ----- ----- -----
|   2 |   5 |  11 |   7 |
\ ----- ----- ----- -----
|   8 |  15 |  12 |   1 |
\ ----- ----- ----- -----

How can I fixed this. It's seems to work only with 10-15.

Answer 1

From documentation on *printf:

In general:

. followed by integer number or *, or neither that specifies precision of the conversion.

And for %d:

Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are ​0​ the conversion results in no characters.

The specifier to use is either "%-2.0d" or %2.0d, depending on if you want the number left- or right-justified, respectively.

#include <stdio.h>

int main(void) {
    printf("Left-justified:\n");
    printf("| %-2.0d |\n", 6);
    printf("| %-2.0d |\n", 11);
    printf("| %-2.0d |\n", 0);

    printf("Right-justified:\n");
    printf("| %2.0d |\n", 3);
    printf("| %2.0d |\n", 14);
    printf("| %2.0d |\n", 0);
}

Output:

Left-justified:
| 6  |
| 11 |
|    |
Right-justified:
|  3 |
| 14 |
|    |

---

A note about the precision specifier:

If neither a number nor * is used, the precision is taken as zero.

This means the form of "%-2.d" would also work.