# Applied Programming/Conditions/C Sharp

## conditions.cs

```/// <summary>
/// This program asks the user for a Fahrenheit temperature,
/// converts the given temperature to Celsius,
/// and displays the results.
///
///Input:
///     Fahrenheit temperature
///
/// Output:
///     Fahrenheit temperature
///    Celsius temperature
///
/// Example:
///    Enter Fahrenheit temperature:
///    100
///    100.0° Fahrenheit is 37.8° Celsius
///
/// References:
///     https://www.mathsisfun.com/temperature-conversion.html
///     https://en.wikibooks.org/wiki/C_Sharp_Programming
///     https://en.wikiversity.org/wiki/Applied_Programming/Functions/Python3
///     https://en.wikiversity.org/wiki/Programming_Fundamentals/Functions/C_Sharp
///     https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/inside-a-program/coding-conventions
///     https://www.dofactory.com/reference/csharp-coding-standards
/// </summary>

using System;

class MainClass
{
const int TemperatureDifference = 32;
const double TemperatureRatio = 5.0 / 9.0;
const double AbsoluteZero = -459.67;

/// <summary>Runs the main program logic.</summary>
public static void Main (string[] args)
{
var fahrenheit = GetFahrenheit();
var celsius = ConvertFahrenheitToCelsius(fahrenheit);
DisplayResult(fahrenheit, celsius);
}

/// <summary>Gets Fahrenheit temperature.</summary>
/// <returns>Returns Fahrenheit temperature.</returns>
/// <exception cref="System.ArgumentOutOfRangeException">
///    Thrown when entered temperature is below absolute zero.
/// </exception>
/// <exception cref="System.FormatException">
///    Thrown when entered temperature is not a valid floating point value.
/// </exception>
private static double GetFahrenheit()
{
Console.WriteLine("Enter Fahrenheit temperature: ");

try
{
var fahrenheit = Convert.ToDouble(input);
if (fahrenheit < AbsoluteZero)
{
Console.WriteLine("Fahrenheit temperature cannot be below absolute zero.");
Console.WriteLine(\$"ArgumentOutOfRangeException: '{fahrenheit}' is invalid.");
Environment.Exit(1);
}

return fahrenheit;
}
catch (System.FormatException)
{
Console.WriteLine("Fahrenheit temperature must be a floating point value.");
Console.WriteLine(\$"FormatException: '{input}' is invalid.");
Environment.Exit(2);
return 0; //Never used
}
}

/// <summary>Calculates Celsius temperature.</summary>
/// <param name="fahrenheit">Fahrenheit temperature.</param>
/// <returns>Returns Celsius temperature.</returns>
private static double ConvertFahrenheitToCelsius(double fahrenheit)
{
System.Diagnostics.Debug.Assert(fahrenheit >= AbsoluteZero);

var celsius = (fahrenheit - TemperatureDifference) * TemperatureRatio;

return celsius;
}

/// <summary>Displays conversion results.</summary>
/// <param name="fahrenheit">Fahrenheit temperature.</param>
/// <param name="fahrenheit">Celsius temperature.</param>
private static void DisplayResult(double fahrenheit, double celsius)
{
Console.WriteLine(fahrenheit.ToString() + "° Fahrenheit is " + celsius + "° Celsius");
}
}
```

## Try It

Copy and paste the code above into one of the following free online development environments or use your own C# compiler / interpreter / IDE.