【正确答案】set talk off
   input to a
   input to b
   input to c
   s=(a+b+C) /2
   if a+b＞c and a+c＞b and b+c＞0 and a＞0 and b＞0 and c＞0
   area=sqrt(s*(s-A) *(s-B) *(s-C) )
   ? "三角形面积为",s
   else
   ? "不能构成三角形"
   endif
   set talk on