11. Write a program to demonstrate Simpson's 1/3 rule.

        /* Program to execte Simpson's 1/3 rule*/
	#include<stdio.h>
	#include<conio.h>
	#include<math.h>
	float calc ( float );
	void main()
	{
	    float x0,xn,h,y;
	    int i,sn;
	    printf("Enter values of x0, xn and number of sub-intervals: ");
	    scanf("%f%f%d", &x0, &xn, &sn);
	    if(sn%2==0) {
	
	        h=(xn-x0)/sn;
	        y=calc(x0) + calc(xn);
	        for(i =1; i < sn; i ++) {
	            if(i%2==0)
	                y +=2*calc(x0+i*h);
	            else
	                y +=4*calc(x0+i*h);
	        }
	        y=(h/3)*y;
	
	        printf("Value of integral is %f",y);
	        getch();
	    } else
	        printf("Unsuitable number of intervals");
	}
	float calc(float x)
	{
	    return 1/(1+x*x);
	}