参考答案：

#include <iostream>//普通版
using namespace std;
const int N = 1010;
char a[N][N];
int b[N][N];
int main()
{
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            cin >> a[i][j];
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            int sum = 0;
            if (a[i][j + 1] == '*') ++ sum;
            if (a[i][j - 1] == '*') ++ sum;
            if (a[i - 1][j] == '*') ++ sum;
            if (a[i + 1][j] == '*') ++ sum;
            if (a[i - 1][j - 1] == '*') ++ sum;
            if (a[i - 1][j + 1] == '*') ++ sum;
            if (a[i + 1][j - 1] == '*') ++ sum;
            if (a[i + 1][j + 1] == '*') ++ sum;
            b[i][j] = sum;
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            if (a[i][j] != '*') printf("%d", b[i][j]);
            else printf("*");
        }
        printf("\n");
    }
    return 0;
}

#include <iostream>//升级版
using namespace std;
const int N = 1010;
char a[N][N];
int b[N][N];
int dx[] = {0,1,1,1,0,-1,-1,-1};//偏移量
int dy[] = {1,1,0,-1,-1,-1,0,1};
int main()
{
    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            cin >> a[i][j];
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            int sum = 0;
            for (int k = 0; k < 8; ++k)
            {
                int x = i + dx[k],y = j + dy[k];
                if (a[x][y] == '*') ++sum;
            }
            b[i][j] = sum;
        }
    }
    for (int i = 1; i <= n; ++i)
    {
        for (int j = 1; j <= m; ++j)
        {
            if (a[i][j] != '*') printf("%d", b[i][j]);
            else printf("*");
        }
        printf("\n");
    }
    return 0;
}