trapezoidal method

#include<stdio.h>
double f(double x)
{
    return (1/(1+(x*x)));
}
void main()
{
    double x0,xn,sum,a,temp,h;
    int n,i;
    printf("enter the limits of the integral x0 and xn\n");
    scanf("%lf %lf",&x0,&xn);
    printf("\nenter the number of intervals\n");
    scanf("%d",&n);
    h=(xn-x0)/n;
    sum=f(x0)+f(xn);
    for(i=1;i<=n-1;i++)
    {
        a=x0+(i*h);
        sum=sum+(2*f(a));
        printf("%.6lf \t %.6lf\n",a,f(a));
    }
    temp=(h/2)*sum;
    printf("the answer is %.6lf\n",temp);
}

OUTPUT:
enter the limits of the integral x0 and xn
0
1

enter the number of intervals
6
0.166667         0.972973
0.333333         0.900000
0.500000         0.800000
0.666667         0.692308
0.833333         0.590164
the answer is 0.784241
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