# Numerical Methods: Integration of given function using Simpson’s 1/3 rule in C

Source Code:

//integration of given function using Simpson's 3/8 rule
#include<stdio.h>
float y(float x){
return 1/(1+x*x); //function of which integration is to be calculated
}
int main(){
float x0,xn,h,s;
int i,n,j,flag;
printf("Enter x0, xn, no. of subintervals: ");
scanf("%f%f%d",&x0,&xn,&n);
h = (xn-x0)/n;
s = y(x0)+y(xn);
for(i = 1; i<=n-1;i++){
for(j=1;j<=n-1;j++){
if(i==3*j){
flag = 1;
break;
}
else
flag = 0;
}
if(flag==0)
s += 3*y(x0+i*h);
else
s += 2*y(x0+i*h);
}
printf("Value of integral is %6.4f\n",(3*h/8)*s);
return 0;
}
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### 5 Responses

1. Unknown says:

this program is not correct — for a correct solution use this link — http://www.codewithc.com/c-program-for-simpson-1-3-rule/

2. Anonymous says:

this is correct program

3. Anonymous says:

Instead of return 1/1+(x*x),it should be written as return f because every function is different for different problems

4. Anonymous says:

Can you please tell me why we have to use i=3 in the for loop in initilization part with increment i=i+2.

5. Primo Raj says:

How to plot corresponding area of the integral in Simpson 1/3 rule with c program? 