我的思路是网格的四周全部置为'*'，设置sign数组记录起始格

#include <stdio.h>
#include <cstring>

char a[20][20];
int sign[20][20];
int n = 1;

int main()
{
    int r, c, cnt, yes, first = 1;

    while(scanf("%d",&r)==1)
    {
        memset(sign,0,sizeof(sign));
        cnt = 1;
        yes = 0;
        if(r == 0) break;
        scanf("%d",&c);
        getchar();
        for(int i = 1; i <= r; i ++)
            {
                for(int j = 1; j <= c; j ++)
                 {scanf("%c",&a[i][j]);}
                getchar();
            }

        for(int i = 0; i <= r+1; i ++)
          a[i][0] = a[i][c+1] = '*';
        for(int j = 0; j <= c+1; j++)
          a[0][j] = a[r+1][j] = '*';
        for(int i = 1; i <= r; i++)
          for(int j = 1; j <= c; j++)
              if((a[i-1][j] == '*' || a[i][j-1] == '*')&&a[i][j] !='*')
                    sign[i][j] = cnt ++;
        if(!first)
           printf("\n");
        first = 0;
        printf("puzzle #%d:\nAcross\n",n);
        for(int i = 1; i <= r; i ++)
            for(int j = 1; j <= c; j ++)
                {
                    if(sign[i][j]) printf("%3d.",sign[i][j]);
                    while(a[i][j] != '*')
                    {
                        printf("%c",a[i][j]);
                        j ++;
                        yes = 1;
                    }
                    if(yes)
                    {
                        printf("\n");
                        yes = 0;
                    }
                 }
        printf("Down\n");
        for(int i = 1; i <= r; i ++)
            for(int j = 1; j <= c; j ++)
                {
                    int m = i;
                    if(sign[i][j]) printf("%3d.",sign[i][j]);
                    while(a[i][j] != '*')
                    {
                        printf("%c",a[i][j]);
                        a[i][j] = '*';
                        sign[i][j] = 0;
                        yes = 1;
                        i ++;
                    }
                    if(yes)
                    {
                        printf("\n");
                        yes = 0;
                    }
                    i = m;
                 }
                 n++;
    }

    return 0;
}