View Compilation Error

0_0_18592424_27585.cpp: In function 'void dfs(int)':
0_0_18592424_27585.cpp:21:12: error: 'mark' was not declared in this scope
         if(mark[i]) continue;
            ^
0_0_18592424_27585.cpp:23:16: error: 'mark' was not declared in this scope
             if(mark[j]) continue;
                ^