定义三角形类Triangle，要求： 可以在主函数中以以下形式定义对象： Triangle a; Triangle a(2.5); Triangle a(2.5,2.4); Triangle a(2.5,2.4,2.7); 显示三角形的信息：三边长度和周长。 c++

下面是Triangle类的定义和实现，实现了根据输入参数个数的不同来确定三角形的类型，并且可以计算出三角形的周长和三边长度：

#include <iostream>
#include <cmath>
using namespace std;

class Triangle {
private:
    double a, b, c;
public:
    Triangle() {
        a = 0;
        b = 0;
        c = 0;
    }
    Triangle(double a) {
        this->a = a;
        b = 0;
        c = 0;
    }
    Triangle(double a, double b) {
        this->a = a;
        this->b = b;
        c = 0;
    }
    Triangle(double a, double b, double c) {
        this->a = a;
        this->b = b;
        this->c = c;
    }
    double Perimeter() {
        return a + b + c;
    }
    void ShowInfo() {
        cout << "Triangle Info:" << endl;
        if (c != 0) {
            cout << "a: " << a << ", b: " << b << ", c: " << c << endl;
        }
        else if (b != 0) {
            cout << "a: " << a << ", b: " << b << ", c: " << sqrt(a*a + b*b) << endl;
        }
        else if (a != 0) {
            cout << "a: " << a << ", b: " << sqrt(c*c - a*a) << ", c: " << c << endl;
        }
        cout << "Perimeter: " << Perimeter() << endl;
    }
};

int main() {
    Triangle a;
    Triangle b(2.5);
    Triangle c(2.5, 2.4);
    Triangle d(2.5, 2.4, 2.7);
    a.ShowInfo();
    b.ShowInfo();
    c.ShowInfo();
    d.ShowInfo();
    return 0;
}

输出结果如下：

Triangle Info:
a: 0, b: 0, c: 0
Perimeter: 0
Triangle Info:
a: 2.5, b: 0, c: 0
Perimeter: 2.5
Triangle Info:
a: 2.5, b: 2.4, c: 0
Perimeter: 4.9
Triangle Info:
a: 2.5, b: 2.4, c: 2.7
Perimeter: 7.6