Simpson's one third

#include<stdio.h>
#include<conio.h>
float f(float x)
{
    return(1/(1+x));
}
void main()
{
    int i,n;
    float x0,xn,h,y[20],so,se,ans,x[20];

    printf("\n Enter values of x0,xn,h: ");

    scanf("%f%f%f",&x0,&xn,&h);

    n=(xn-x0)/h;

    if(n%2==1)
    {
        n=n+1;
    }

    h=(xn-x0)/n;

    printf("\n Refined value of n and h are:%d %f\n",n,h);

    printf("\n Y values: \n");

    for(i=0; i<=n; i++)
    {
        x[i]=x0+i*h;
        y[i]=f(x[i]);
        printf("\n %f\n",y[i]);
    }

    so=0;
    se=0;

    for(i=1; i<n; i++)
    {
        if(i%2==1)
        {
            so=so+y[i];
        }
        else
        {
            se=se+y[i];
        }

    }

    ans=h/3*(y[0]+y[n]+4*so+2*se);

    printf("\n Final integration is %f",ans);

    getch();
}