How to array the numbers like a bowtie shape in c - c

Question

I'm trying to arrange numbers in a nxn(n is odd number) matrix with bow tie shapes. (like fig.)
Trying to 5x5 matrix set coordinates but no result.
my code:
bowtie {
int a[5][5] = {{
0,
},
{
0,
},
{
0,
},
{
0,
},
{
0,
}};
int i, j;
int num = 1;
for (i = 0; i < 5; i++) {
if (i <= 2) // y>=0 - coordinate(2d)
{
for (j = i; j <= 2; j++) // x<=0, y>=0 Quadrant 2
{
a[i][j] = num;
num++;
}
for (j = 4 - i; j > i; j++) // Quadrant 1
{
a[i][j] = num;
num++;
}
} else // y<0
for (j = 4 - i; j <= 4 - i; j++) // Quadrant 3
{
a[i][j] = num;
num++;
}
for (j = i; j >= i; j++) // Quadrant 2
{
a[i][j] = num;
num++;
}
}
for (i = 0; i < 5; j++) {
for (j = 0; j < 5; j++) {
printf("%d\t", a[i][j]);
}
printf("\n");
}
}

Answer 1

The loop
for (j = 4 - i; j > i; j++) // Quadrant 1
is wrong because j starts at 4 (i valuing 0) being the last valid index then never stop to grow producing an undefined behavior when you go out of the array
The loop
for (j = 4 - i; j <= 4 - i; j++) // Quadrant 3
is strange because the last possible value is the first one, so this is not a loop but just its body executed with j = 4 - i
The loop
for (j = i; j >= i; j++) // Quadrant 2
is like the first and makes j incompatible with the array dimensions
A proposal where the size in given in argument and can be odd or even :
#include <stdio.h>
int main(int argc, char ** argv)
{
if (argc != 2)
printf("Usage %s <size>\n", *argv);
else {
int n;
if ((sscanf(argv[1], "%d", &n) != 1) || (n < 1))
fprintf(stderr, "invalid size %s\n", argv[1]);
else {
int a[n][n];
int v = 0; /* the value 1.. to put in the cells */
int empty; /* the empty height */
int i,j;
/* first half and may be center */
empty = -1;
for (j = 0; j <= (n-1)/2; ++j) {
empty += 1;
for (i = 0; i != empty; ++i)
a[i][j] = a[n - i - 1][j] = 0;
for (int k = n - empty*2; k; --k)
a[i++][j] = ++v;
}
if ((n & 1) == 0)
empty += 1;
/* second half */
for (; j < n; ++j) {
empty -= 1;
for (i = 0; i != empty; ++i)
a[i][j] = a[n - i - 1][j] = 0;
for (int k = n - empty*2; k; --k)
a[i++][j] = ++v;
}
/* show result */
for (i = 0; i != n; ++i) {
for (j = 0; j != n; ++j) {
if (a[i][j] == 0)
fputs(" ", stdout); /* witdh = 4 compatible with a size up to 43 */
else
printf("% 4d", a[i][j]); /* width = 4 compatible with a size up to 43 */
}
putchar('\n');
}
}
}
return 0;
}
Compilation and executions :
pi#raspberrypi:/tmp $ gcc -pedantic -Wextra -Wall b.c
pi#raspberrypi:/tmp $ ./a.out 1
1
pi#raspberrypi:/tmp $ ./a.out 2
1 3
2 4
pi#raspberrypi:/tmp $ ./a.out 3
1 5
2 4 6
3 7
pi#raspberrypi:/tmp $ ./a.out 4
1 9
2 5 7 10
3 6 8 11
4 12
pi#raspberrypi:/tmp $ ./a.out 5
1 13
2 6 10 14
3 7 9 11 15
4 8 12 16
5 17
pi#raspberrypi:/tmp $ ./a.out 6
1 19
2 7 15 20
3 8 11 13 16 21
4 9 12 14 17 22
5 10 18 23
6 24
pi#raspberrypi:/tmp $ ./a.out 7
1 25
2 8 20 26
3 9 13 17 21 27
4 10 14 16 18 22 28
5 11 15 19 23 29
6 12 24 30
7 31
If you do not accept even size
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char ** argv)
{
if (argc != 2)
printf("Usage %s <size>\n", *argv);
else {
int n;
if ((sscanf(argv[1], "%d", &n) != 1) || (n < 1) || ((n & 1) == 0))
fprintf(stderr, "invalid size %s\n", argv[1]);
else {
int a[n][n];
int v = 1; /* the value 1.. to put in the cells */
int empty; /* the empty height */
/* first half more center */
empty = -1;
for (int j = 0; j <= n/2; ++j) {
int i;
empty += 1;
for (i = 0; i != empty; ++i)
a[i][j] = a[n - i - 1][j] = 0;
for (int k = n - empty*2; k; --k)
a[i++][j] = v++;
}
/* second half */
for (int j = n/2 + 1; j < n; ++j) {
int i;
empty -= 1;
for (i = 0; i != empty; ++i)
a[i][j] = a[n - i - 1][j] = 0;
for (int k = n - empty*2; k; --k)
a[i++][j] = v++;
}
/* show result */
for (int i = 0; i != n; ++i) {
for (int j = 0; j != n; ++j) {
if (a[i][j] == 0)
fputs(" ", stdout);
else
printf("% 4d", a[i][j]);
}
putchar('\n');
}
}
}
return 0;
}
Compilation and executions :
pi#raspberrypi:/tmp $ gcc -pedantic -Wextra -Wall o.c
pi#raspberrypi:/tmp $ ./a.out
Usage ./a.out <size>
pi#raspberrypi:/tmp $ ./a.out 1
1
pi#raspberrypi:/tmp $ ./a.out 2
invalid size 2
pi#raspberrypi:/tmp $ ./a.out 3
1 5
2 4 6
3 7
pi#raspberrypi:/tmp $ ./a.out 5
1 13
2 6 10 14
3 7 9 11 15
4 8 12 16
5 17
pi#raspberrypi:/tmp $ ./a.out 17
1 145
2 18 130 146
3 19 33 117 131 147
4 20 34 46 106 118 132 148
5 21 35 47 57 97 107 119 133 149
6 22 36 48 58 66 90 98 108 120 134 150
7 23 37 49 59 67 73 85 91 99 109 121 135 151
8 24 38 50 60 68 74 78 82 86 92 100 110 122 136 152
9 25 39 51 61 69 75 79 81 83 87 93 101 111 123 137 153
10 26 40 52 62 70 76 80 84 88 94 102 112 124 138 154
11 27 41 53 63 71 77 89 95 103 113 125 139 155
12 28 42 54 64 72 96 104 114 126 140 156
13 29 43 55 65 105 115 127 141 157
14 30 44 56 116 128 142 158
15 31 45 129 143 159
16 32 144 160
17 161
pi#raspberrypi:/tmp $
From you remark
'int a[n][n];' has problem.
probably you compiled in C++ rather than C, but it is easy to change that :
replace int a[n][n]; by int * a = malloc(n*n*sizeof(int));
replace each form a[x][y] by a[(x)*n+y]
add a free(a); at the end
For instance if I do that on the proposal only accepting odd size :
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char ** argv)
{
if (argc != 2)
printf("Usage %s <size>\n", *argv);
else {
int n;
if ((sscanf(argv[1], "%d", &n) != 1) || (n < 1) || ((n & 1) == 0))
fprintf(stderr, "invalid size %s\n", argv[1]);
else {
int * a = malloc(n*n*sizeof(int));
int v = 1; /* the value 1.. to put in the cells */
int empty; /* the empty height */
/* first half more center */
empty = -1;
for (int j = 0; j <= n/2; ++j) {
int i;
empty += 1;
for (i = 0; i != empty; ++i)
a[i*n+j] = a[(n - i - 1)*n+j] = 0;
for (int k = n - empty*2; k; --k)
a[i++*n+j] = v++;
}
/* second half */
for (int j = n/2 + 1; j < n; ++j) {
int i;
empty -= 1;
for (i = 0; i != empty; ++i)
a[i*n+j] = a[(n - i - 1)*n+j] = 0;
for (int k = n - empty*2; k; --k)
a[i++*n+j] = v++;
}
/* show result */
for (int i = 0; i != n; ++i) {
for (int j = 0; j != n; ++j) {
if (a[i*n+j] == 0)
fputs(" ", stdout);
else
printf("% 4d", a[i*n+j]);
}
putchar('\n');
}
free(a);
}
}
return 0;
}