View Compilation Error

0_0_17172697_24407.cpp:5:12: error: array bound is not an integer constant before ']' token
 int  a[maxn];
            ^
0_0_17172697_24407.cpp: In function 'void solve()':
0_0_17172697_24407.cpp:11:25: error: 'a' was not declared in this scope
             scanf("%d",&a[i]);
                         ^
0_0_17172697_24407.cpp:16:15: error: 'a' was not declared in this scope
         ans^=(a[i]+a[j]);
               ^
0_0_17172697_24407.cpp:19:35: error: 'a' was not declared in this scope
         for(int i=1;i<x;i++)ans^=(a[x]+a[i])^(y+a[i]);
                                   ^
0_0_17172697_24407.cpp:20:38: error: 'a' was not declared in this scope
         for(int i=x+1;i<=n;i++)ans^=(a[x]+a[i])^(y+a[i]);
                                      ^
0_0_17172697_24407.cpp:21:9: error: 'a' was not declared in this scope
         a[x]=y;
         ^