View Compilation Error

0_0_13156173_21368.cpp:12:7: error: 'M' was not declared in this scope
 }tree[M*4];
       ^
0_0_13156173_21368.cpp: In function 'void btree(int, int, int)':
0_0_13156173_21368.cpp:15:5: error: 'tree' was not declared in this scope
     tree[rt].left=left;
     ^
0_0_13156173_21368.cpp: In function 'void query(int, int, int, int, int)':
0_0_13156173_21368.cpp:31:14: error: 'tree' was not declared in this scope
         ans+=tree[rt].sum;
              ^
0_0_13156173_21368.cpp:34:13: error: 'tree' was not declared in this scope
     int mid=tree[rt].mid();
             ^
0_0_13156173_21368.cpp: In function 'void update(int, int, int, int, int)':
0_0_13156173_21368.cpp:49:9: error: 'tree' was not declared in this scope
         tree[rt].sum+=add;
         ^
0_0_13156173_21368.cpp:52:13: error: 'tree' was not declared in this scope
     int mid=tree[rt].mid();
             ^