View Compilation Error

0_0_37948424_27408.cpp: In function 'void init()':
0_0_37948424_27408.cpp:11:12: error: 'st' was not declared in this scope
     memset(st,0,sizeof st);
            ^
0_0_37948424_27408.cpp: In function 'int main()':
0_0_37948424_27408.cpp:43:7: error: 'a' was not declared in this scope
   vis[a] = vis[b] = 1;
       ^
0_0_37948424_27408.cpp:43:16: error: 'b' was not declared in this scope
   vis[a] = vis[b] = 1;
                ^