Language: C++

#include<iostream>
using namespace std;
int main()
{
	int i,j,H,W;
	char inic,midc;
	while(1)
	{
		inic = "o";
		midc = "o";
		cin >> H >>W;
		if ((H==0) && (W==0)) break;
		for (i=0;i<H;i++)
		{
			switch(inic){
			  case "o":
				inic = "#";
				break;
			  case "#":
				inic = ".";
				break;
			  case ".":
				inic = "#";
				break;
			}
			cout << inic;
			midc = inic;
			for (j=0; j<W; j++)
			{
				switch(midc){
				  case "#":
					midc = ".";
					break;
				  case ".":
					midc = "#";
					break;
				}
				cout << midc;
			}
			cout << endl;
		}
		cout << endl;
	}
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:24: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
    9 |                 inic = "o";
      |                        ^~~
      |                        |
      |                        const char*
a.cc:10:24: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   10 |                 midc = "o";
      |                        ^~~
      |                        |
      |                        const char*
a.cc:16:32: error: conversion from 'const char*' to 'int' in a converted constant expression
   16 |                           case "o":
      |                                ^~~
a.cc:16:32: error: could not convert '"o"' from 'const char [2]' to 'int'
   16 |                           case "o":
      |                                ^~~
      |                                |
      |                                const char [2]
a.cc:17:40: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   17 |                                 inic = "#";
      |                                        ^~~
      |                                        |
      |                                        const char*
a.cc:19:32: error: conversion from 'const char*' to 'int' in a converted constant expression
   19 |                           case "#":
      |                                ^~~
a.cc:19:32: error: could not convert '"#"' from 'const char [2]' to 'int'
   19 |                           case "#":
      |                                ^~~
      |                                |
      |                                const char [2]
a.cc:20:40: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   20 |                                 inic = ".";
      |                                        ^~~
      |                                        |
      |                                        const char*
a.cc:22:32: error: conversion from 'const char*' to 'int' in a converted constant expression
   22 |                           case ".":
      |                                ^~~
a.cc:22:32: error: could not convert '"."' from 'const char [2]' to 'int'
   22 |                           case ".":
      |                                ^~~
      |                                |
      |                                const char [2]
a.cc:23:40: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   23 |                                 inic = "#";
      |                                        ^~~
      |                                        |
      |                                        const char*
a.cc:31:40: error: conversion from 'const char*' to 'int' in a converted constant expression
   31 |                                   case "#":
      |                                        ^~~
a.cc:31:40: error: could not convert '"#"' from 'const char [2]' to 'int'
   31 |                                   case "#":
      |                                        ^~~
      |                                        |
      |                                        const char [2]
a.cc:32:48: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   32 |                                         midc = ".";
      |                                                ^~~
      |                                                |
      |                                                const char*
a.cc:34:40: error: conversion from 'const char*' to 'int' in a converted constant expression
   34 |                                   case ".":
      |                                        ^~~
a.cc:34:40: error: could not convert '"."' from 'const char [2]' to 'int'
   34 |                                   case ".":
      |                                        ^~~
      |                                        |
      |                                        const char [2]
a.cc:35:48: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   35 |                                         midc = "#";
      |                                                ^~~
      |                                                |
      |                                                const char*