*为乘号 /为除号
(7-7)*7+7/7=1
(7+7)/7+7-7=2
(7+7/7+7/7=3
7-(7+7+7)/7=4
7-7/7-7/7=5
7-(7/7)*(7/7)=6
7+7+7-7-7=7
7+(7/7)*(7/7)=8