by Dinesh Thakur Category: Control Structures

The trapezoidal rule is the simplest method to approximate the definite integral of a function f(x) over the interval [a, b]. Given N equally space points (with a spacing of h) X0, X1, ..., XN such that X0 = a and XN = b, the integral of f(x) can be approximated as the sum


The program TRAPEZOID.C integrates a function whose pointer is passed to it using the trapezoidal rule.

#include <stdlib.h>

#include <math.h>
#include <stdio.h>
/* function prototypes */
double integrate(double(*func)(double),
double xa, double xb, int intervals);
double foobar(double x);
double myfunc(double x);
 double foobar(double x)
     return (exp(x)-2.0);
   double myfunc(double x)
    return x*x;
               double integrate(double(*yfunc)(double),
     double xa, double xb, int nintervals)
                double sum=0.0, x, hwidth;
                int iter;
                x = xa;
                hwidth = (xb-xa)/nintervals;
                x+= hwidth;
                sum+= yfunc(x);
                   sum+= yfunc(xa)/2.0;
                   sum+= yfunc(xb)/2.0;
                   return sum*hwidth;
int main()
       double integral, pi;
       printf("integral foobar [0.0,2.0] = %lg\n\n",integral);
       pi = acos(-1.0) ;
       integral=integrate(sin,0.0,pi ,300);
       printf("integral sin [0.0,pi] = %lg\n\n",integral);
       printf("integral myfunc [0.0,3.0] = %lg\n\n",integral);
            printf("integral myfunc [0.0,3.0] = %lg\n\n",integral);
              return 0;

C calculating Integration using Trapezoidal Rule

About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.

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