P268 1

<img src="http://img.blog.csdn.net/20150610194457571?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvWXVTb25nNDg2OQ==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />#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; }