View Compilation Error

0_0_21580165_31973.cpp: In function 'int main()':
0_0_21580165_31973.cpp:21:17: error: 'num' was not declared in this scope
                 num.push_back(i);
                 ^
0_0_21580165_31973.cpp:27:19: error: 'num' was not declared in this scope
         int len = num.size();
                   ^