foo.cpp: In function 'void scan(int)':
foo.cpp:14:45: warning: array subscript has type 'char' [-Wchar-subscripts]
     for (i = 0; i < l >> 1; ++i) swap(n[t][i], n[t][l - i - 1]);
                                             ^
foo.cpp:14:45: error: invalid initialization of reference of type 'int&' from expression of type 'char'
foo.cpp:6:13: error: in passing argument 1 of 'void swap(int&, int&)'
 inline void swap(int &x, int &y) {
             ^
foo.cpp:15:42: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (f) for (i = 0; i < l; ++i) n[t][i] = -n[t][i];
                                          ^
foo.cpp:15:53: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (f) for (i = 0; i < l; ++i) n[t][i] = -n[t][i];
                                                     ^
foo.cpp: In function 'int main()':
foo.cpp:21:37: warning: array subscript has type 'char' [-Wchar-subscripts]
     for (i = 0; i < len; ++i) n[0][i] += n[1][i];
                                     ^
foo.cpp:21:48: warning: array subscript has type 'char' [-Wchar-subscripts]
     for (i = 0; i < len; ++i) n[0][i] += n[1][i];
                                                ^
foo.cpp:23:74: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (n[0][len - 1] < 0) for (putchar('-'), i = 0; i < len; ++i) n[0][i] = -n[0][i];
                                                                          ^
foo.cpp:23:85: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (n[0][len - 1] < 0) for (putchar('-'), i = 0; i < len; ++i) n[0][i] = -n[0][i];
                                                                                     ^
foo.cpp:25:22: warning: array subscript has type 'char' [-Wchar-subscripts]
         while (n[0][i] < 0) n[0][i] += 10, --n[0][i + 1];
                      ^
foo.cpp:25:35: warning: array subscript has type 'char' [-Wchar-subscripts]
         while (n[0][i] < 0) n[0][i] += 10, --n[0][i + 1];
                                   ^
foo.cpp:26:22: warning: array subscript has type 'char' [-Wchar-subscripts]
         while (n[0][i] > 9) n[0][i] -= 10, ++n[0][i + 1];
                      ^
foo.cpp:26:35: warning: array subscript has type 'char' [-Wchar-subscripts]
         while (n[0][i] > 9) n[0][i] -= 10, ++n[0][i + 1];
                                   ^
foo.cpp:28:17: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (n[0][len]) ++len;
                 ^
foo.cpp:30:46: warning: array subscript has type 'char' [-Wchar-subscripts]
     for (i = len - 1; ~i; --i) putchar(n[0][i] + '0');
                                              ^