/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:9:4: error: 'i' was not declared in this scope
  s[i][j]=0;
    ^
/in/foo.cc:9:7: error: 'j' was not declared in this scope
  s[i][j]=0;
       ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:22:16: warning: format '%c' expects argument of type 'char*', but argument 2 has type 'int' [-Wformat=]
    scanf("%c",a);
                ^