View Compilation Error

0_0_24385336_8897.cpp:8:9: error: expected primary-expression before ']' token
 }a[maxn*];//线段树; 
         ^
0_0_24385336_8897.cpp: In function 'void Bulid(int, int, int)':
0_0_24385336_8897.cpp:43:2: error: 'a' was not declared in this scope
  a[rt].l=s;a[rt].r=t;
  ^
0_0_24385336_8897.cpp: In function 'void Work(int, int, int)':
0_0_24385336_8897.cpp:52:5: error: 'a' was not declared in this scope
  if(a[rt].l==a[rt].r){
     ^
0_0_24385336_8897.cpp:57:5: error: 'a' was not declared in this scope
  if(a[x].sum>=k)Work(x,num,k);
     ^
0_0_24385336_8897.cpp:61:2: error: 'a' was not declared in this scope
  a[rt].sum=a[x].sum+a[y].sum;
  ^