第七章第一题

#include <iostream>#include <cmath>using namespace std;int main(){double a,b,c,s,area; cout<<"please input a,b,c:"; cin>>a>>b>>c; if (a+b<=c)  cerr<<"a+b<=c,error!"<<endl; else if(b+c<=a)  cerr<<"b+c<=a,error!"<<endl; else if (c+a<=b)  cerr<<"c+a<=b,error!"<<endl; else  {  s=(a+b+c)/2;   area=sqrt(s*(s-a)*(s-b)*(s-c));      cout<<"area="<<area<<endl;   } return 0;}