Was asked to solve the problem on https://www.facebook.com/ProgrammersCreateLife/photos/a.241809332534619.55240.241806149201604/1662976313751240/?type=3 Could be improved even more, but that's for when I'll have my own blog.

test.c

#include <stdio.h>
#include <stdlib.h>

int main()
{
	const int sz = 10;

	for (int i = 0; i < sz; i++) {
		for (int j = 0; j < sz; j++) {
			if (i == 0 || i == sz - 1)
				printf("#");
			else if (j == 0 || j == sz - 1)
				printf("#");
			else if (i == j || i + j == sz - 1)
				printf("#");
			else
				printf(" ");
		}
		printf("\n");
	}

	return 0;
}