指针调用函数实例

2020/12/10 C++

思修课无聊搞出来的东西

题目:

手撸代码

#include <iostream>
#include <cmath>
using namespace std;
double Tn(double a, double b, double n,int sumtype);
double f1(double x);
double f2(double x);
double f3(double x);
const int PI = 3.1415926;

int main()
{
    double n, a, b;int sumtype;
    cout << "Please enter a b n,sum 1 or 2 or 3" << endl;
    cin >> b >> a >> n >> sumtype;
    double result = Tn(a, b, n,sumtype);
    cout << "result is " << result << endl;
}

double Tn(double a, double b,double n, int sumtype)
{
    double h = (b - a) / n;
    double (*f)(double);
    switch (sumtype)
    {
    case 1: f = f1; break;
    case 2: f = f2; break;
    case 3: f = f3; break;
    default: abort();
        break;
    }
    double fa = f(a); double fb = f(b); double sum = 0;
    for (int i=1; i < n; i++)
    {
        sum += f(a + i*h);
    }
    return h * (f(a) + f(b)) / 2 + h * sum;
}

double f1(double x)
{
    return 4 / (1 + x * x);
}

double f2(double x)
{
    return sqrt(1 + x * x);
}

double f3(double x)
{
    return sin(x);
}

注意，22行定义指针时，要带上形参(double)，且要用(*p)，因为优先级的原因，否则会报错!!!

然后就可以愉快地求积分啦!再也不用担心数学作业不会啦!(逃——)

这个是第三个函数的结果，可以发现，在π精度很高，和切片n很多的时候，得到了正确的积分::one:

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指针调用函数实例