View Compilation Error

0_0_26243657_18156.cpp: In function 'long long int dfs(int, char)':
0_0_26243657_18156.cpp:11:42: error: 'at' was not declared in this scope
             if (s[i] + goal == 'A'+ 'B') at = 'C';
                                          ^
0_0_26243657_18156.cpp:12:43: error: 'at' was not declared in this scope
             if (s[i] + goal == 'A' + 'C') at = 'B';
                                           ^
0_0_26243657_18156.cpp:13:43: error: 'at' was not declared in this scope
             if (s[i] + goal == 'B' + 'C') at = 'A';
                                           ^