even strings of an array in backwards way - c

Question

I am trying to print an array in order to the even strings print backwards but the not even string in usual way. What do I do wrong with it?
For example:
1 0 3
9 7 3
5 7 8
and I need it:
1 0 3
3 7 9
5 7 8
But I also have a problem with filling an array in spiral way; how should I take a center of an array? Please, could you give an idea — how should I do this? And the array must be square. For example:
1 2 3
4 5 6
7 8 9
but I need it:
3 2 9
4 1 8
5 6 7
My code so far:
#include <stdio.h>
#include <stdlib.h>
int main()
{
int a[10][10],n,m,i,j;
printf("Enter m: ");
scanf("%d",&m);
printf("Enter n: ");
scanf("%d",&n);
for(i=0;i<m;i++){
for(j=0;j<m;j++){
printf("a[%d][%d]: ",i+1,j+1);
scanf("%d",&a[i][j]);
}
}
// in usual order
for(i=0;i<m;i++){
for(j=0;j<n;j++){
printf("%d ",a[i][j]);
}
printf("\n");
}
for(i=0;i<m;i++){
for(j=0;j<n;j++){
if(i%2 != 0){
printf("%d ",a[i][j]);
}
else {
printf("%d ",a[n-i+1][j]);
}
}
printf("\n");
}
return 0;
}

Answer 1

example of filling an array in spiral
#include <stdio.h>
#include <string.h>
typedef enum {
N, W, S, E
} Dir;
typedef struct walker {
int row, col;
Dir dir;
int steps;
} Walker;
Walker go_forward(Walker walker){
switch(walker.dir){
case N:
walker.row -= 1;
break;
case W:
walker.col -= 1;
break;
case S:
walker.row += 1;
break;
case E:
walker.col += 1;
break;
}
return walker;
}
Walker proceed_left(Walker walker){
walker.dir = (walker.dir + 1) % 4;//turn left
walker = go_forward(walker);
return walker;
}
int main(void){
int n;
for(;;){
printf("Enter n(0 < n < 10): ");fflush(stdout);
int ret_s = scanf("%d", &n);
if(ret_s == 1){
if(0 < n && n < 10)
break;
} else if(ret_s == 0)
while(getchar() != '\n');//clear input
else //if(ret_s == EOF)
return 0;
}
int a[n][n];
memset(a, 0, sizeof(a));//zero clear
Walker walker = { .row = n / 2, .col = n / 2, .dir = E, .steps = 0 };
for(;;){
walker.steps += 1;
a[walker.row][walker.col] = walker.steps;
if(walker.steps == n * n)//goal
break;
Walker left = proceed_left(walker);
if(a[left.row][left.col] == 0)//left side is vacant
walker = left;
else
walker = go_forward(walker);
}
for(int r = 0; r < n; ++r){
for(int c = 0; c < n; ++c){
if(c)
putchar(' ');
printf("%2d", a[r][c]);
}
puts("");
}
}

Answer 2

Here is a program that includes the function spiral_fill(), which fills a square array with sequential ints, starting from 1 at the center, and proceeding in a counter-clockwise spiral. The function fills the array by first storing a 1 in the center, then filling the L-shaped region above and to the left, then below and to the right, and continuing until the array is filled.
#include <stdio.h>
#define ARR_SZ 3
void spiral_fill(size_t arr_sz, int arr[arr_sz][arr_sz]);
void print_arr(size_t rows, size_t cols, int arr[rows][cols]);
int main(void)
{
int test_arr[ARR_SZ][ARR_SZ];
spiral_fill(ARR_SZ, test_arr);
print_arr(ARR_SZ, ARR_SZ, test_arr);
return 0;
}
void spiral_fill(size_t arr_sz, int arr[arr_sz][arr_sz])
{
int center = arr_sz / 2;
int current = center;
int start_col, stop_col, start_row, stop_row;
size_t layer = 0;
int next_val = 1;
arr[center][center] = next_val++;
++layer;
while (layer < arr_sz) {
if (layer % 2) { // For odd layers, fill upper L
current -= layer;
start_col = center + layer / 2;
stop_col = center - (layer + 1) / 2;
for (int j = start_col; j >= stop_col; j--) {
arr[current][j] = next_val++;
}
start_row = center - layer / 2;
stop_row = center + layer / 2;
for (int i = start_row; i <= stop_row; i++) {
arr[i][current] = next_val++;
}
++layer;
} else { // For even layers, fill lower L
current += layer;
start_col = center - layer / 2;
stop_col = center + layer / 2;
for (int j = start_col; j <= stop_col; j++) {
arr[current][j] = next_val++;
}
start_row = center + (layer - 1) / 2;
stop_row = center - layer / 2;
for (int i = start_row; i >= stop_row ; i--) {
arr[i][current] = next_val++;
}
++layer;
}
}
}
void print_arr(size_t rows, size_t cols, int arr[rows][cols])
{
for (size_t i = 0; i < rows; i++) {
for (size_t j = 0; j < cols; j++) {
printf("%-5d ", arr[i][j]);
}
putchar('\n');
}
}
Here is a 3X3 array:
3 2 9
4 1 8
5 6 7
Here is a 6X6 array:
31 30 29 28 27 26
32 13 12 11 10 25
33 14 3 2 9 24
34 15 4 1 8 23
35 16 5 6 7 22
36 17 18 19 20 21