运行时输入：
abc*+de*f+g*+
1 BinTree CreateExprTree() 2 { 3 std::stack<BinTree> S; 4 BinTree T, Tl, Tr, BT; 5 6 ElementType dt; 7 scanf_s("%c", &dt); 8 while (dt >= 'a' && dt <= 'z') 9 { 10 T = (BinTree)malloc(sizeof(struct TNode)); 11 T->Data = dt; 12 T->Left = T->Right = NULL; 13 S.push(T); 14 scanf_s("%c", &dt); 15 } 16 while (dt != ' ') 17 { 18 if (dt >= 'a' && dt <= 'z') 19 { 20 T = (BinTree)malloc(sizeof(struct TNode)); 21 T->Data = dt; 22 T->Left = T->Right = NULL; 23 S.push(T); 24 scanf_s("%c", &dt); 25 } 26 else 27 { 28 T = (BinTree)malloc(sizeof(struct TNode)); 29 T->Data = dt; 30 Tr = S.top(); 31 S.pop(); 32 Tl = S.top(); 33 S.pop(); 34 T->Left = Tl; 35 T->Right = Tr; 36 S.push(T); 37 scanf_s("%c", &dt); 38 } 39 40 } 41 BT = S.top(); 42 43 return BT; 44 }