用c＋＋编写一个函数分别求三角形、矩形，圆形的图形面积

好的，以下是用C++编写的函数分别求三角形、矩形和圆形的面积：

#include <iostream>
#include <cmath>

using namespace std;

const double PI = 3.14159265358979323846;

double triangleArea(double base, double height) {
    return 0.5 * base * height;
}

double rectangleArea(double length, double width) {
    return length * width;
}

double circleArea(double radius) {
    return PI * pow(radius, 2);
}

int main() {
    double base, height, length, width, radius;
    cout << "Enter base and height of triangle: ";
    cin >> base >> height;
    cout << "Area of triangle: " << triangleArea(base, height) << endl;
    cout << "Enter length and width of rectangle: ";
    cin >> length >> width;
    cout << "Area of rectangle: " << rectangleArea(length, width) << endl;
    cout << "Enter radius of circle: ";
    cin >> radius;
    cout << "Area of circle: " << circleArea(radius) << endl;
    return 0;
}

希望这个函数可以帮助你计算图形的面积。