View Compilation Error

0_0_17023986_3241.cpp: In function 'int main()':
0_0_17023986_3241.cpp:19:36: error: 'a' was not declared in this scope
                  c2[j+i] += c1[i] ;a
                                    ^
0_0_17023986_3241.cpp:20:28: error: 'i' was not declared in this scope
          for ( int i = 0 ; i <= num[2]*2+num[1]*1 ; ++ i )
                            ^