View Compilation Error

0_0_28460919_9486.cpp: In function 'int main()':
0_0_28460919_9486.cpp:7:11: error: conflicting declaration 'int a [100]'
  int a[100];
           ^
0_0_28460919_9486.cpp:5:6: note: previous declaration as 'int a'
  int a,b;
      ^
0_0_28460919_9486.cpp:13:22: error: invalid types 'int[int]' for array subscript
       scanf("%d",&a[i]);
                      ^
0_0_28460919_9486.cpp:14:15: error: invalid types 'int[int]' for array subscript
       num+=a[i];
               ^