三角形面积计算
#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
int main()
{
double a,b,c;
cout<<"please enter a,b,c:";
cin>>a>>b>>c;
if(a+b>c&&b+c>a&&c+a>b)
{
double s,area;
s=(a+b+c)/2;
area=sqrt(s*(s-a)*(s-b)*(s-c));
cout<<setiosflags(ios::fixed)<<setprecision(4);
cout<<"area="<<area<<endl;
}
else cout<<"it isn't a trilateral!\n"<<endl;
return 0;}