Language: C++

using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;
 
namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
 
            return;
        }
 
        public void Solve(ConsoleInput cin)
        {
            var H = cin.ReadInt;
            var W = cin.ReadInt;
            var S = cin.ReadStrArray(H);
 
            char[,] map = new char[H, W];
 
            for (int i = 0; i < H; i++)
            {
                var tmp = S[i].ToCharArray();
                for (int j = 0; j < W; j++)
                {
                    map[i, j] = tmp[j];
                }
            }
 
            //for (int i = 0; i < H; i++)
            //{
            //    for (int j = 0; j < W; j++)
            //    {
            //        Write(map[i, j]);
            //    }
            //    Write("\n");
            //}
 
            int[] dx = new int[] {  1,  0, -1,  0,  1, -1, -1,  1 };
            int[] dy = new int[] {  0,  1,  0, -1,  1,  1, -1, -1 };
 
 
            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    if (map[i, j] == '#')
                    {
                        continue;
                    }
 
                    int num = 0;
                    for (int d = 0; d < 8; d++)
                    {
                        int ni = i + dy[d];
                        int nj = j + dx[d];
 
                        if (ni < 0 || ni >= H) continue;
                        if (nj < 0 || nj >= W) continue;
                        if (map[ni, nj] == '#') num++;
 
                    }
 
                    map[i, j] = (char)(num + '0');
 
                }
            }
 
            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    Write(map[i, j]);
                }
                Write("\n");
            }
 
        }
 
 
    }
 
    public static class Extensions
    {
        public static string Reverse(this string sourse)
        {
            char[] chrAry = sourse.ToCharArray();
            Array.Reverse(chrAry);
            return new string(chrAry);
        }
    }
 
    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }
}
using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));

            return;
        }

        public void Solve(ConsoleInput cin)
        {
            var H = cin.ReadInt;
            var W = cin.ReadInt;
            var S = cin.ReadStrArray(H);

            char[,] map = new char[H, W];

            for (int i = 0; i < H; i++)
            {
                var tmp = S[i].ToCharArray();
                for (int j = 0; j < W; j++)
                {
                    map[i, j] = tmp[j];
                }
            }

            //for (int i = 0; i < H; i++)
            //{
            //    for (int j = 0; j < W; j++)
            //    {
            //        Write(map[i, j]);
            //    }
            //    Write("\n");
            //}

            int[] dx = new int[] {  1,  0, -1,  0,  1, -1, -1,  1 };
            int[] dy = new int[] {  0,  1,  0, -1,  1,  1, -1, -1 };


            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    if (map[i, j] == '#')
                    {
                        continue;
                    }

                    int num = 0;
                    for (int d = 0; d < 8; d++)
                    {
                        int ni = i + dy[d];
                        int nj = j + dx[d];

                        if (ni < 0 || ni >= H) continue;
                        if (nj < 0 || nj >= W) continue;
                        if (map[ni, nj] == '#') num++;

                    }

                    map[i, j] = (char)(num + '0');

                }
            }

            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    Write(map[i, j]);
                }
                Write("\n");
            }

        }


    }

    public static class Extensions
    {
        public static string Reverse(this string sourse)
        {
            char[] chrAry = sourse.ToCharArray();
            Array.Reverse(chrAry);
            return new string(chrAry);
        }
    }

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }
}
Submission

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Text;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Collections;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:6:7: error: expected nested-name-specifier before 'static'
    6 | using static System.Console;
      |       ^~~~~~
a.cc:7:7: error: expected nested-name-specifier before 'static'
    7 | using static System.Math;
      |       ^~~~~~
a.cc:11:5: error: expected unqualified-id before 'public'
   11 |     public class Program
      |     ^~~~~~
a.cc:90:5: error: expected unqualified-id before 'public'
   90 |     public static class Extensions
      |     ^~~~~~
a.cc:100:5: error: expected unqualified-id before 'public'
  100 |     public class ConsoleInput
      |     ^~~~~~
a.cc:131:7: error: expected nested-name-specifier before 'System'
  131 | using System;
      |       ^~~~~~
a.cc:132:7: error: expected nested-name-specifier before 'System'
  132 | using System.Text;
      |       ^~~~~~
a.cc:133:7: error: expected nested-name-specifier before 'System'
  133 | using System.Linq;
      |       ^~~~~~
a.cc:134:7: error: expected nested-name-specifier before 'System'
  134 | using System.Collections;
      |       ^~~~~~
a.cc:135:7: error: expected nested-name-specifier before 'System'
  135 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:136:7: error: expected nested-name-specifier before 'static'
  136 | using static System.Console;
      |       ^~~~~~
a.cc:137:7: error: expected nested-name-specifier before 'static'
  137 | using static System.Math;
      |       ^~~~~~
a.cc:141:5: error: expected unqualified-id before 'public'
  141 |     public class Program
      |     ^~~~~~
a.cc:220:5: error: expected unqualified-id before 'public'
  220 |     public static class Extensions
      |     ^~~~~~
a.cc:230:5: error: expected unqualified-id before 'public'
  230 |     public class ConsoleInput
      |     ^~~~~~
a.cc:261:1: error: 'Submission' does not name a type
  261 | Submission
      | ^~~~~~~~~~