runner% cat mult_table.c
#include <stdio.h>
#include <stdlib.h>

#define MAXNUM 13

void main(void)
{
        int i, j;
        printf("  * |");
        for (j = 0; j < MAXNUM; j++)
                printf("%4i", j);
        printf("\n----|");
        for (j = 0; j < MAXNUM; j++)
                printf("----");
        printf("\n");
        for (i = 0; i < MAXNUM; i++) {
                printf("%4i|", i);
                for (j = 0; j < MAXNUM; j++)
                        printf("%4i", i*j);
                printf("\n");
        }
}

runner% cat mult_table_2.c
#include <stdio.h>
#include <stdlib.h>

#define MAXNUM 13

void print_header(void);
void create_table(int m[][MAXNUM]);
void print_table(int m[][MAXNUM]);

void main(void)
{
        int m[MAXNUM][MAXNUM];
        print_header();
        create_table(m);
        print_table(m);
        exit(0);
}

void print_header(void)
{
        int j;
        printf("  * |");
        for (j = 0; j < MAXNUM; j++)
                printf("%4i", j);
        printf("\n----|");
        for (j = 0; j < MAXNUM; j++)
                printf("----");
        printf("\n");
}

void create_table(int m[][MAXNUM])
{
        int i, j;
        for (i = 0; i < MAXNUM; i++)
                for (j = 0; j < MAXNUM; j++)
                        m[i][j] = i*j;
}
        
void print_table(int m[][MAXNUM])
{
        int i, j;
        for (i = 0; i < MAXNUM; i++) {
                printf("%4i|", i);
                for (j = 0; j < MAXNUM; j++)
                        printf("%4i", m[i][j]);
                printf("\n");
        }
}
runner% mult_table
  * |   0   1   2   3   4   5   6   7   8   9  10  11  12
----|----------------------------------------------------
   0|   0   0   0   0   0   0   0   0   0   0   0   0   0
   1|   0   1   2   3   4   5   6   7   8   9  10  11  12
   2|   0   2   4   6   8  10  12  14  16  18  20  22  24
   3|   0   3   6   9  12  15  18  21  24  27  30  33  36
   4|   0   4   8  12  16  20  24  28  32  36  40  44  48
   5|   0   5  10  15  20  25  30  35  40  45  50  55  60
   6|   0   6  12  18  24  30  36  42  48  54  60  66  72
   7|   0   7  14  21  28  35  42  49  56  63  70  77  84
   8|   0   8  16  24  32  40  48  56  64  72  80  88  96
   9|   0   9  18  27  36  45  54  63  72  81  90  99 108
  10|   0  10  20  30  40  50  60  70  80  90 100 110 120
  11|   0  11  22  33  44  55  66  77  88  99 110 121 132
  12|   0  12  24  36  48  60  72  84  96 108 120 132 144
runner% mult_table > out.text
runner% mult_table_2 >out2.text
runner% diff out.text out2.text
runner%