Add Integrate.cpp

Integrate.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+#include <string>
+using std::cout, std::string, std::endl;
+
+class Integrate
+{
+protected:
+    double a, b;
+    int n;
+
+public:
+    virtual double fun(double x) = 0;
+    Integrate(double _a, double _b, int _n = 10000) : a{_a}, b{_b}, n{_n} {}
+    double integrate()
+    {
+        double result{(fun(a) + fun(b)) / 2};
+        double h{(b - a) / n};
+        for (int i{1}; i < n; i++)
+            result += fun(a + i * h);
+        result *= h;
+        return result;
+    }
+};
+
+class F1 : public Integrate
+{
+public:
+    using Integrate::Integrate;
+    double fun(double x) override
+    {
+        return x;
+    }
+};
+
+class F2 : public Integrate
+{
+public:
+    using Integrate::Integrate;
+    double fun(double x) override
+    {
+        return x * x;
+    }
+};
+
+class F3 : public Integrate
+{
+public:
+    using Integrate::Integrate;
+    double fun(double x) override
+    {
+        return x * x * x;
+    }
+};
+
+int compare(Integrate &a, Integrate &b)
+{
+    // 比较两个积分对象值的结果，a大返回1，b大返回-1，相同返回0
+    if (a.integrate() > b.integrate())
+        return 1;
+    if (a.integrate() < b.integrate())
+        return -1;
+    return 0;
+}
+
+int main()
+{
+    F1 f1{0, 1};
+    F2 f2{0, 1};
+    F3 f3{0, 1};
+    cout << f1.integrate() << ' ' << f2.integrate() << ' ' << f3.integrate() << '\n';
+    // 设计通用接口compare，积分类的任意派生对象可进行比较
+    cout << compare(f1, f2) << '\n';
+    cout << compare(f1, f3) << '\n';
+    cout << compare(f2, f3) << '\n';
+}