首先判断给出的3条边能否构成三角形。如可以构成。则计算并输出该三角形的面积，否则要求重新输入。当输入-1时结束程序-First of all, given to determine whether the three constitute a triangle edge. Such as may constitute. Are calculated and output in the triangle area, and failing that, to re-enter. When you e