View Compilation Error

0_0_25358132_3557.cpp:26:7: error: 'maxn' was not declared in this scope
 int a[maxn];
       ^
0_0_25358132_3557.cpp: In function 'int main()':
0_0_25358132_3557.cpp:32:16: error: 'a' was not declared in this scope
         memset(a,0,sizeof(a));
                ^
0_0_25358132_3557.cpp:40:38: error: expected primary-expression before '=' token
             if (a[i+1] < a[i]) sum + =(a[i]-a[i+1])*4 + 5;
                                      ^