Write a program to find the area under the curve y = f(x) between x = a and x = b, integrate y = f(x) between the limits of a and b. The area under a curve between two points can be found by doing a definite integral between the two points.

Solution :

#include
float    start_point,            /* GLOBAL VARIABLES */

    end_point,
    total_area;
int    numtraps;
main( )
{
   void    input(void);
   float    find_area(float a,float b,int n); /* prototype */


   print(“AREA UNDER A CURVE”);
   input( );
   total_area = find_area(start_point, end_point, numtraps);
   printf(“TOTAL AREA = %f”, total_area);
}
void input(void)
{
   printf(“\n Enter lower limit:”);
   scanf(“%f”, &start_point);
   printf(“Enter upper limit:”);
   scanf(“%f”, &end_point);
   printf(“Enter number of trapezoids:”);
   scanf(“%d”, &numtraps);
}
float find_area(float a, float b, int n)
{
      floatbase, lower, h1, h2;    /* LOCAL VARIABLES */
float function_x(float x);    /* prototype */
float trap_area(float h1,float h2,floatbase);/*prototype*/
base = (b-1)/n;
         lower = a;
       for(lower =a; lower <= b-base; lower = lower + base)
    {
    h1  =  function_x(lower);
             h1  =  function_x(lower + base);
             total_area += trap_area(h1, h2, base);
    }
return(total_area);
    float trap_area(float height_1,float height_2,floatbase)
        {
       float area;    /* LOCAL VARIABLE */

       area = 0.5 * (height_1 + height_2) * base;
         return(area);
    }
    float function_x(float x)
    {
         /* F(X) = X * X + 1 */
return(x*x + 1);
    }
   
Output

    AREA UNDER A CURVE
    Enter lower limit: 0
    Enter upper limit:  3
    Enter number of trapezoids: 30
    TOTAL AREA   =  12.005000

    AREA UNDER A CURVE
    Enter lower limit: 0
    Enter upper limit: 3
    Enter number of trapezoids: 100
    TOTAL AREA = 12.000438