Unit 2 การกำหนดช่วงตัวเลขของรากสมการ

/*Program 2.3 : ScanRoot.c
  Purpose: Search for intervals that containing one or an odd number
         of roots, or poles, or both.
  Author : Wachara Rodsumrid.
  Last update : 07 MAR 94
**************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double tf(double);        /* Target Function */

void main()
{
double a,            /* starting value of x             */
      b,            /* ending value of x               */
      h,            /* constant increment of interval  */
      x,            /* any value of x                  */
      y,            /* functional value at x           */
      yb;
char buffer[255];
int i,found;
      clrscr();
      printf("\n\t\tSearch for Interval that containing roots.");
      printf("\n\t\t==========================================");
      printf("\nStarting value of x : ");gets(buffer);
      a =atof(buffer);
      printf("Ending value of x : ");gets(buffer);
      b = atof(buffer);
      printf("Increment of x    : ");gets(buffer);
      h  = atof(buffer);
      if ( a > b) {
	  x = b; b= a; a= x;
      }
      i = 0; x = a; found=0;
      while ( x < b) {
          y  = tf(x);
          yb = tf(x+h);
          i+=1;
          if ( y*yb < 0 ) {
             printf("\nInterval that contain root(s) : [%g,  %g]",x,x+h);
             found +=1;
          }
          x += h;
      }
      printf("\n\n Found %d interval !!\n",found);
      exit(0);
}
double tf(double h)
{
	return(3.284*exp(-(h-36089)/20806) - 7.35);
}