View Compilation Error

0_0_32801133_8930.cpp: In function 'void build(int, int, int)':
0_0_32801133_8930.cpp:24:33: error: void value not ignored as it ought to be
     int a = build(i << 1, l, mid);
                                 ^
0_0_32801133_8930.cpp:25:39: error: void value not ignored as it ought to be
     int b = build(i << 1 | 1,mid + 1,r);
                                       ^
0_0_32801133_8930.cpp:27:34: error: return-statement with a value, in function returning 'void' [-fpermissive]
     return tree[i].maxn = max(a,b);
                                  ^