View Compilation Error

0_0_17633122_12083.cpp: In function 'int main()':
0_0_17633122_12083.cpp:13:16: error: invalid types 'double [21][double]' for array subscript
             a[i]=(i-1)*(a[i-1]+a[i-2]);
                ^
0_0_17633122_12083.cpp:13:30: error: invalid types 'double [21][double]' for array subscript
             a[i]=(i-1)*(a[i-1]+a[i-2]);
                              ^
0_0_17633122_12083.cpp:13:37: error: invalid types 'double [21][double]' for array subscript
             a[i]=(i-1)*(a[i-1]+a[i-2]);
                                     ^
0_0_17633122_12083.cpp:19:31: error: invalid types 'double [21][double]' for array subscript
         printf("%.2lf%%\n",a[n]/s*100);
                               ^