1 #include<iostream>
 2 #include<cmath>
 3 #include<iomanip>
 4 using namespace std;
 5 
 6 int main()
 7 {
 8     double a, b, c;
 9 
10     cout << "please enter a, b and c:";
11     cin >> a >> b >> c;
12     
13     if (a + b > c && b + c > a && c + a > b)//
 
判斷能否構成三角形
14     {
15         double s, area;
16 
17         s = 0.5 * (a + b + c);
18         area = sqrt(s * (s-a) * (s-b) * (s-c));
19 
20         cout << setiosflags(ios::fixed) << setprecision(4);
21         cout << "area = " << area << endl;
22     }
23     else cout << "
 
it is not a trilateral!" << endl;
24     while (1);
25     return 0;
26 }

三角形面積公式