C program for Simpson's 1/3 Rule

Before Starting the program let us know about the Simpson's 1/3 rule and How it works?

Simpson’s 1/3 Rule The trapezoidal rule was based on approximating the integrand by a first-order polynomial and then integrating the polynomial over an interval of integration. Simpson’s 1/3 rule is an extension of the Trapezoidal rule where the integrand is approximated by a second-order polynomial.

Simple Simpsons one third Formula

Composite Simpsons one third formula

Application :

It is used when it is very difficult to solve the given integral mathematically.

This rule gives approximation easily without actually knowing the integration rules

C program to for Composite Simpsons 1/3 rule

#include<stdio.h>
#include<conio.h>
#include<math.h>
//#define f(x) sqrt(1-((x)*(x)))
//#define f(x) exp(-1*(x*x))
//#define f(x) (cos(x)*cos(x))
//#define f(x) sin(x)
#define f(x) exp(-1*(x/2))
int main(){
 
 float a,h,x0,xn,fx0,fxn,term,v;
 int i,k;
 printf("Composite Simpson's 1/3 rule'");
 printf("\nEnter Lower and Upper Limit \n");
 scanf("%f%f",&x0,&xn);
 printf("\nEnter number of segments (should be multiple of 2)\n");
 scanf("%d",&k);
 h=(xn-x0)/k;
 fx0=f(x0);
 fxn=f(xn);
 term=f(x0)+f(xn);
 
 for(i=1;i<=(k-1);i=i+2){
  a=x0+i*h;
  term=term+4*(f(a));
 }
 
 for(i=2; i<=(k-2);i=i+2){
  a=x0+i*h;
  term=term+2*(f(a));
 }
 
 v=h/3*term;
 
 printf("\nValue of Integration= %f\n",v);
 return 0;
}

C program for Simpsons 1/3 rule

#include<stdio.h>
#include<conio.h>
#include<math.h>
//#define f(x) 3*(x)*(x)+2*(x)-5
//#define f(x) sin(x)
//#define f(x) exp(-1*(x/2))
#define f(x) 3*x*x
int main(){
 
 float h,x0,x1,x2,fx0,fx1,fx2,v;
 int n=2;
 printf("Simpson's 1/3 rule'");
 printf("\nEnter Lower and Upper Limit \n");
 scanf("%f%f",&x0,&x2);
 h=(x2-x0)/n;
 x1=x0+h;
 fx0=f(x0);
 fx1=f(x1);
 fx2=f(x2);
 v=h/3*(fx0+4*fx1+fx2);
 printf("\nValue of Integration= %f\n",v);
 return 0;
}