View Compilation Error

0_0_14647737_29113.cpp: In function 'int main()':
0_0_14647737_29113.cpp:33:13: error: 'i' was not declared in this scope
         for(i = 1 ; i <= n ; i++) {
             ^
0_0_14647737_29113.cpp:36:50: error: 'a' was not declared in this scope
                 x += dp[i]*(dp[i]-1)*(dp[i]-2)/6*a[i] ;
                                                  ^