View Compilation Error

0_0_23777407_22450.cpp: In function 'int main()':
0_0_23777407_22450.cpp:5:6: error: conflicting declaration 'int a'
  int a,b,i;  
      ^
0_0_23777407_22450.cpp:4:15: note: previous declaration as 'long long int a [31]'
     long long a[31];
               ^
0_0_23777407_22450.cpp:11:12: error: lvalue required as decrement operand
     while(a--)
            ^