ernie.WPI.EDU> cat exam3_1.C

// file exam3_1.C, cs2223, D97/98 //
// a program to calculate a square root

// 10Apr98 NW, First version

// includes
#include "headers.h"

// prototype
double unknown(double, double, double); // unknown function

// global variable
int counter;

// main
int main ()
	{
	double number;
	while (1) // infinite loop
		{
		cout << "please enter a number greater than 0: ";
		cin >> number;
		if (number <= 0) return 0; // exit criterion
		counter = 0;
		cout << "The answer is " << unknown(number, number, number) << endl;
		cout << "The function was called " << counter << " times" << endl << endl;
		}
	} // end main()

double unknown(double number, double guess, double increment) // unknown function
	{ 
	extern int counter;
	counter++; // count how many times the function was called
	double error = guess * guess - number;
	double abs_error = error < 0 ? -error : error; // absolute value of the error
	if (abs_error < 1.0 / 1048576.0) return guess; // close enough
	double inc2 = increment / 2.0;
	if (error > 0) return unknown(number, guess - inc2, inc2);// positive error
	else  return unknown(number, guess + inc2, inc2);// negative error
	} // end unknown()

// Copyright 1998 Norman Wittels

ernie.WPI.EDU> g++ exam3_1.C

ernie.WPI.EDU> a.out

please enter a number greater than 0: 1
The answer is 1
The function was called 1 times

please enter a number greater than 0: 2
The answer is 1.41421
The function was called 23 times

please enter a number greater than 0: 3
The answer is 1.73205
The function was called 24 times

please enter a number greater than 0: 8
The answer is 2.82843
The function was called 26 times

please enter a number greater than 0: 19
The answer is 4.3589
The function was called 27 times

please enter a number greater than 0: 25
The answer is 5
The function was called 27 times

please enter a number greater than 0: 26
The answer is 5.09902
The function was called 27 times

please enter a number greater than 0: 199
The answer is 14.1067
The function was called 33 times

please enter a number greater than 0: 1000
The answer is 31.6228
The function was called 35 times

please enter a number greater than 0: 0.5
The answer is 0.707107
The function was called 20 times

please enter a number greater than 0: -3

ernie.WPI.EDU>