UNIX for Advanced & Expert Users

/* *************************************************

Purpose:      Solve for the roots of the quadratic equation,
                       y = a x^2 + b x + c
                 by means of the quadratic formula,
                 root = (-b +or- sqrt(b^2 -4. a c))/(2. a)

Variables:    a, b, c + Real coefficients of quadratic equation.
                 d = Discriminant
                 root1, root2  = Real roots or real part of complex roots.
                 root1i,root2i = Imaginary part of complex roots.
Input:        Values of coefficients in file 167w02cp1c.dat
Output:       Tabulated values of coefficients and roots, with
                 proper heading and captions, in the UNIX xterm    window.

************************************************** */

#include <stdio.h>      /* Access input/output functions */
#include <math.h>       /* Access math functions */

void main(void)
{
/* Float all variables */

         double a, b, c, d, root1, root2;
         double root1i,root2i;

         FILE *fp;

         fp = fopen ("167w02cp1c.dat","r");       /* Open input file */
         if (fp==NULL)                       /* Test for file not open */
{                                                /* Terminate the program */
                 puts("\nData file 167w02cp1c.dat has failed to open.");
                 puts("\nProgram cp1.c is terminated.\n");
                 return;
}

puts("\n                 Class goes here");
puts("\n                     2002");
puts("\n                    Name goes here");
puts("\n                   Problem No. 1");
puts("\n                 Roots of Quadratic Equations");
printf("\n      a         b         c       root1   ");
printf("  Root2");
printf("\n -------------------------------------------------");
printf(" ----------------------------------------");

while (! feof(fp))                             /* Start of Loop */
{
   fscanf (fp,"%1f%*c%1f%*c%1f",&a,&b,&c);     /* Input Values */

             if (feof(fp))                   /* Looks for end of file */
                      {
                      puts("\n End of Data. Program cp1 complete,");
                      break;
}

if (a==0. || b==0. && c==0.)    /* Check for invalid data */
        {
        printf("\n%10.3f%10.3f%10.3f    invalid data",a,b,c);
        }
        else
                d = ((b*b)-(4*a*c));    /* Compute the Discriminant */

/* Compute roots for when the discriminant is positive */

        if (d>1.0*pow(10,-6))
        {

        root1 = ((-b)+pow(d,0.5))/(2*a);
        root2 = ((-b)-pow(d,0.5))/(2*a);

        printf("\n%10.3f%10.3f%10.3f%13.3f%13.3f",
                 a, b, c, root1, root2);
                 /* Print Values */
        }

/* Compute roots for when the discriminant is negative */

else if (d<-1.0*pow(10,-6))
{

        root1 = -b/(2.*a); root2 = root1;

        root1i = sqrt(-d)/(2.*a);
        root2i = -root1i;

        printf("\n%10.3f%10.3f%10.3f%8.3f%8.3f%8.3f%8.3fi",
           a, b, c, root1,root1i,root2,root2i);        /* Print Values */
        }

else
        {
         root1 = (-b)/(2*a);
         root2 = root1;

         printf("\n%10.3f%10.3f%10.3f%13.3f%13.3f",
                a,b,c,root1,root2);
}
}
}               /* End While Loop */