12-1等腰三角形的面积 (100 满分) 题目描述 输入一个三角形三条边长，判断是否是等腰三角形并计算其面积。注意若输入数据非等腰三角形数据，要求使用exception处理。

#include
#include
#include

using namespace std;

/完善此函数/
double calArea(double a, double b, double c) {
}

int main(){
double a, b, c;
cin >> a >> b >> c;
try{
double area = calArea(a, b, c);
cout << area << endl;
}catch(exception& e){
cout << e.what() << endl;
}
}

输入描述
输入三角形三条边

输出描述
若输入确实为等腰三角形，输出其面积，保留两位小数。

若不是等腰三角形，抛出异常并输出字符串"The input is illegal"

样例输入
3 4 5

样例输出
The input is illegal

#include 
#include 
#include 
#include 
using namespace std;

double calArea(double a, double b, double c) throw (invalid_argument)
{

	if (a <= 0 || b <= 0 || c <= 0)
		throw invalid_argument("The input is illegal");
	if (a + b <= c || b + c <= a || c + a <= b)
		throw invalid_argument("The input is illegal");
	if (a != b && a != c && b != c)
		throw invalid_argument("The input is illegal");
	else
	{
		double p = (a + b + c) / 2;
		return  sqrt(p*(p - a)*(p - b)*(p - c));
	}
}

int main(){
    double a, b, c;
    cin >> a >> b >> c;
    try{
        double area = calArea(a, b, c);
        cout << fixed << setprecision(2) << area << endl;
    }catch(exception& e){
        cout << e.what() << endl;
    }
}