View Compilation Error

0_0_31938774_32631.cpp:6:7: error: 'maxn' was not declared in this scope
 int a[maxn];
       ^
0_0_31938774_32631.cpp: In function 'int main()':
0_0_31938774_32631.cpp:11:21: error: 'a' was not declared in this scope
         scanf("%d",&a[i]);
                     ^
0_0_31938774_32631.cpp:13:13: error: 'a' was not declared in this scope
         sum=a[0];
             ^