Trapezoidal Rule C++

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

float y(float x)
{
return 1/(1+x*x);
}

int main()
{
float x0,xn,h,s;
int i,n;

cout<<"Enter the x0,xn, no. of subintervals"<<endl;
cin>>x0>>xn>>n;
cout<<fixed;

h=(xn-x0)/n;
s=y(x0)+y(xn);

for(i=1;i<=n-1;i++)
s += 2*y(x0+i*h);

cout<<"Value of integral is ";
cout<<setw(6)<<setprecision(4);
cout<<(h/2)*s<<endl;
return 0;
}