exercise9.c

// C Primer Plus

// Chapter 5 Exercise 9:

// Write a program that requests the user to enter a Fahrenheit temperature. The
// program should read the temperature as a type double number and pass it as an
// argument to a user-supplied function called Temperatures(). This function should
// calculate the Celsius equivalent and the Kelvin equivalent and display all three
// temperatures with a precision of two places to the right of the decimal. It
// should identify each value with the temperature scale it represents. Here is the
// formula for converting Fahrenheit to Celsius:
//     Celsius = 5.0 / 9.0 * (Fahrenheit - 32.0)
// The Kelvin scale, commonly used in science, is a scale in which 0 represents
// absolute zero, the lower limit to possible temperatures. Here is the formula for
// converting Celsius to Kelvin:
//     Kelvin = Celsius + 273.16
// The Temperatures() function should use const to create symbolic representations
// of the three constants that appear in the conversions. The main() function
// should use a loop to allow the user to enter temperatures repeatedly, stopping
// when a q or other nonnumeric value is entered. Use the fact that scanf() returns
// the number of items read, so it will return 1 if it reads a number, but it won’t
// return 1 if the user enters q. The == operator tests for equality, so you can
// use it to compare the return value of scanf() with 1.

#include <stdio.h>

void Temperatures(double fahr); // prototype declaration of Temperatures

int main(void)
{
	double fahr;
	printf("This program converts fahrenheit to celsius and kelvin.\n");
	printf("Enter a temperature in degrees fahrenheit (q to quit): ");
	while (scanf("%lf", &fahr) == 1) // continue executing loop if user enters valid number
	{
		Temperatures(fahr); // convert fahr to celsius and kelvin

		// prompt for new input
		printf("Enter a temperature in degrees fahrenheit (q to quit): ");
	}

	printf("bye\n");
}

void Temperatures(double fahr)
{
	const double FAHR_TO_CEL_SCALE = 5.0 / 9.0;
	const double FAHR_TO_CEL_OFFSET = -32.0;
	const double CEL_TO_KEL_OFFSET = 273.16;

	double celsius = (fahr + FAHR_TO_CEL_OFFSET) * FAHR_TO_CEL_SCALE;
	double kelvin = celsius + CEL_TO_KEL_OFFSET;

	printf("%.2f degrees fahrenheit is %.2f degrees celsius or %.2f degrees kelvin.\n",
			fahr, celsius, kelvin);
}