/*
Program: binary-search-solves-equation.c (Report comments/bugs to chikh@yuntech.edu.tw)
Function: 利用二分搜尋法求方程式之根 
*/
 
#include <stdio.h>
#include <math.h>

//#define f(x) (x)*(x)
#define f(x) x+sin(x)-1
//#define f(x) ((x)*exp(x))*((x)*exp(x))

double binary_search(double);
   
int main()
{   
	float value, answer;
	
	printf("Enter the value ==> ");
	scanf("%f",&value);
	answer = binary_search(value);
    printf("The root = %g (Check if f(%g)=%g == %g?)\n",answer,answer,f(answer),value);
    
    return 0;
}

double binary_search(double y)
{
	double a, b, mid, temp;
	
	a = 0; 
	b = y+2;
	
	while (1) {
		if (a > b) break;
		mid = (a+b)/2.0;
		temp = f(mid);
		if (fabs(temp-y) < 1e-10) return mid;
		if (temp < y) 
			a = mid;
		else
			b = mid;		
	}
	
	return -1;
}