1
#include <iostream>
2
#include <cmath>
3
using namespace std;
4
double Tn(double a, double b, double n,int sumtype);
5
double f1(double x);
6
double f2(double x);
7
double f3(double x);
8
const int PI = 3.1415926;
9

10
int main()
11
{
12
  double n, a, b;int sumtype;
13
  cout << "Please enter a b n,sum 1 or 2 or 3" << endl;
14
  cin >> b >> a >> n >> sumtype;
15
  double result = Tn(a, b, n,sumtype);
16
  cout << "result is " << result << endl;
17
}
18

19
double Tn(double a, double b,double n, int sumtype)
20
{
21
  double h = (b - a) / n;
22
  double (*f)(double);
23
  switch (sumtype)
24
  {
25
  case 1: f = f1; break;
26
  case 2: f = f2; break;
27
  case 3: f = f3; break;
28
  default: abort();
29
    break;
30
  }
31
  double fa = f(a); double fb = f(b); double sum = 0;
32
  for (int i=1; i < n; i++)
33
  {
34
    sum += f(a + i*h);
35
  }
36
  return h * (f(a) + f(b)) / 2 + h * sum;
37
}
38

39
double f1(double x)
40
{
41
  return 4 / (1 + x * x);
42
}
43

44
double f2(double x)
45
{
46
  return sqrt(1 + x * x);
47
}
48

49
double f3(double x)
50
{
51
  return sin(x);
52
}