Program3

/*

 *  prog3A.c

 *

 *  Calculates the integral of cos^2(x).

 *

 *  Input command line argument of upper limit between 0 and Pi/2.

 *  Lower limit is set by default to 0.

 */



#include <stdio.h>

#include <stdlib.h>

#include <math.h>

#define NODATA "There was not one argument entered. Exiting...\n"

#define INVALID "The data entered was not valid. Entered value must be between 0 and Pi/2\n"

#define LOWERLIMIT 0

#define MAXLIMIT M_PI/2

#define FILENAME "px270prog3a.dat"

#define RESULT "The integral of (Cos(x))^2 between %lf and %lf is %lf\n"

#define DEBUG 0



void integrate(double *xvalues, double *fvalues, int count, double low , double high, double *integral);



int main(int argc, char* argv[]) {

    /*Values*/

    double a,b,value,dummy;

    double *xvalues, *fvalues,integral;

    /*Counts*/

    int size=0,count=0,entrycount=0;

    /*Flags*/

    int rightnumber=0,validInput;

    /*File*/

    FILE* input;



    /*Set Lower Limit*/

    a = LOWERLIMIT;

    /*Check and then read command line arguments */

    if ((argc < 2)||(argc > 2)){

        printf(NODATA);

        exit(EXIT_FAILURE);

    }

    else {

        sscanf(argv[1],"%lf", &b);

    }

    /*Test for valid input. If not valid, exit*/

    validInput = ((b > LOWERLIMIT) && (b < MAXLIMIT) && (b != EOF));

    if(!validInput){

        printf(INVALID);

        exit(EXIT_FAILURE);

    }

    /*Open file, read data from file*/

    input = fopen(FILENAME,"r");

    /*Scan through the file once, to help work out size of array needed*/

    while (rightnumber == 0){

        fscanf(input," %lf ",&value);

        fscanf(input," %lf ",&dummy);

        count++;
        printf("Count = %d \n",count);

        /*If the value read for x is greater than the upper limit, stop counting data*/

        if (value >= b) {

            rightnumber = 1;

            rewind(input);

        }

    }

    /*Set the size of the arrays*/

    size = (count+1)*(sizeof(double));

    xvalues = (double*)malloc(size);

    fvalues = (double*)malloc(size);

    /*Use fscanf to fill arrays with values*/

    while (entrycount<=count) {

        fscanf(input,"%lf",&xvalues[entrycount]);

        fscanf(input,"%lf",&fvalues[entrycount]);

        entrycount++;
        //printf("Entrycount = %lf, Xvalues = %lf, FXVALues = %lf \n",entrycount,xvalues[entrycount],fvalues[entrycount]);

    }

    fclose(input);

    /*Call integrate function, using pointer for integral, print result*/

    integrate(xvalues,fvalues,count+1,a,b,&integral);

    printf(RESULT,a,b,integral);



    return 0;

}



void integrate(double *xvalues, double *fvalues, int length, double lowlim , double uplim, double *integral){

    double workinginteg;

    int count=0;

    int firstpoint=0;



    while (count<length) {

        /*Check if values within integration limits*/

        if (xvalues[count] <= uplim){

            if (xvalues[count] >= lowlim) {

                if (firstpoint == 0) {

                    /*If the lower limit is not zero, add in the first part. If it is, this part will be zero anyway*/

                    if (count != 0) *integral += (xvalues[count]-lowlim)*(fvalues[count-1]);

                    firstpoint = 1;

                }

                else {

                    /*Add the next part of the integral*/

                    *integral += (xvalues[count]-xvalues[count-1])*(fvalues[count-1]);

                }

            }

        }

        count++;

    }

}