View Compilation Error

0_0_30556685_14904.cpp: In function 'int main()':
0_0_30556685_14904.cpp:5:16: error: conflicting declaration 'long long int a [51]'
  long long a[51]={0,1,2};
                ^
0_0_30556685_14904.cpp:4:8: note: previous declaration as 'int a'
  int n,a,b;
        ^
0_0_30556685_14904.cpp:7:6: error: invalid types 'int[int]' for array subscript
   a[i]=a[i-1]+a[i-2];
      ^
0_0_30556685_14904.cpp:7:13: error: invalid types 'int[int]' for array subscript
   a[i]=a[i-1]+a[i-2];
             ^
0_0_30556685_14904.cpp:7:20: error: invalid types 'int[int]' for array subscript
   a[i]=a[i-1]+a[i-2];
                    ^
0_0_30556685_14904.cpp:11:14: error: invalid types 'int[int]' for array subscript
   cout<<a[b-a]<<endl;  
              ^