Void function not printing to screen. Plz Help!!!

[c++help]

Hi, I am supposed to write code for a program that calculates the wind chill index based on the temperature and wind speed entered by the user. Then I have to use a void function which has to "cout" the effect based on the windchill. I can get the program to output the windchill but can't get the void function to work. Please help. Thanks!

#include <iostream>
#include <cmath>

using namespace std;

double windchill_calculator(double temperature, double windspeed);
void effect(double windchill);

int main()
{
	double w;
	double temperature;
	double windspeed;

do
{
	cout << "Enter the air temperature in degree Celsius: ";
	cin >> temperature;

	cout << "Enter the wind speed in kilometres per hour (km/h): ";
	cin >> windspeed;

	if (windspeed < 0)
		cout << "The windspeed must be greater or equal to 0"<< endl<< endl;

} while (windspeed < 0);


	if (windspeed > 4.8)
		w = windchill_calculator(temperature, windspeed);

	else if (windspeed >= 0 && windspeed <= 4.8)
		w = temperature;

	cout << "The wind chill index is " << w << endl;

	effect(w);

}


double windchill_calculator(double temperature, double windspeed)
{
	double windchill = 13.12 + (0.6215*temperature) - (11.37*(pow(windspeed,0.16))) + (0.3965*temperature*pow(windspeed,0.16));
	return windchill;
}

void effect(double windchill)
{
	if (windchill >= 0 && windchill < -25)
	{
		cout<< "Discomfort"<< endl;
	}
	else if (windchill >= -25 && windchill < -45)
	{
		cout<< "Risk of skin freezing (frostbite)"<< endl;
	}
	else if (windchill >= -45 && windchill < -60)
	{
		cout<< "Exposed skin may freeze within minutes"<< endl;
	}
	else if (windchill >= 60)
	{
		cout<< "Exposed skin may freeze in under 2 minutes"<< endl;
	}

	return;
}

[laserlight]

How does it not work?

(In this case I can see why it does not work, but you should get into the habit.)

[c++help]

Sorry. This is the out put i get when i enter the values -30 and 50 for temperature and windspeed, respectively.

Enter the air temperature in degree Celsius: -30
Enter the wind speed in kilometres per hour (km/h): 50
The wind chill index is -49.0299

[laserlight]

In other words, effect does not seem to print any effect at all, even when it should have printed "Exposed skin may freeze within minutes".

Here's a maths quiz: pick a real number that is greater than or equal to 0, and less than -25. Done? What number did you pick?

[c++help]

I don't get what you mean...

[laserlight]

I don't get what you mean...

Basically, you are specifying your windchill range wrongly. If we draw a real number line:

.          -25                0
<-----------|-----------------|--------------->
<-----------|                 |--------------->
 Region A                         Region B

The only real numbers that satisfy your condition are those that exist in region A and B simultaneously. No such real numbers exist.

A typical way to do this is to start from one extreme first. So, if windchill <= -60, print "Exposed skin may freeze in under 2 minutes". Else, if windchill <= -45, print "Exposed skin may freeze within minutes". This immediately caters for the case where windchill == -50, because -50 is not <= -60, but it is <= -45.