ex.8.6.c

// Function to calculate the absolute value of a number

#include <stdio.h>

double absoluteValue (double x)
{
	if ( x < 0 )
		x = -x;
	return (x);
}

// Function to compute the square root of a number

double squareRoot (double x)
{
	const double	epsilon	= .00001;
	double			guess	= 1.0;

	while ( absoluteValue (guess * guess - x) >= epsilon )
		guess = ( x / guess + guess ) / 2.0;

	return guess;
}

int main (void)
{
	printf ("squareRoot (2.0) = %f\n", squareRoot (2.0));
	printf ("squareRoot (144.0) = %f\n", squareRoot (144.0));
	printf ("squareRoot (17.5) = %f\n", squareRoot (17.5));

	return 0;
}