별 찍기 http://pgr21.com/pb/pb.php?id=qna&no=1478

gistfile1.txt

#include<stdio.h>
int N;
char buf[100];
int main()
{
    scanf("%d", &N);
    for(int i = (N << 1); i >= 1; i--)
    {
        int len = ((i-N) >= 0) * i + ((i-N) < 0) * N;
        int space = N ^ (((i-1) ^ N) & -((i-1) < N));
        for(int j = 0; j < len-space; j++)
           buf[j] = '*';
        buf[len-space] = 0;
        printf("%*s\n", len, buf);
    }
    return 0;
}