View Compilation Error

0_0_20198302_267.cpp: In function 'int main()':
0_0_20198302_267.cpp:16:46: error: 'e' was not declared in this scope
   scanf("%d",&n);pres=-1;for(int i=0;i<n;++i)e[i].clear();
                                              ^
0_0_20198302_267.cpp:24:5: error: 'e' was not declared in this scope
     e[b].push_back(i);e[pres].push_back(i);
     ^
0_0_20198302_267.cpp:42:16: error: 'e' was not declared in this scope
    for(auto&&x:e[p]) {
                ^