#include <stdio.h>
#include<stdlib.h>
int main()
{
    int i,j,num;
    scanf("%d",&num);
    for(i=-num/2;i<=num/2;i++)
    {
        for(j=-num/2;j<=num/2;j++)
        {
            if(abs(i)+abs(j)==num/2)
                printf("*");
            else
                printf(" ");
        }
        puts("");
    }
    return 0;
}

结果：
20
          *
         * *
        *   *
       *     *
      *       *
     *         *
    *           *
   *             *
  *               *
 *                 *
*                   *
 *                 *
  *               *
   *             *
    *           *
     *         *
      *       *
       *     *
        *   *
         * *
          *
Press any key to continue

呵，在群里抄的