Programming Fundamentals/Conditions/BASIC

conditions.bas

' This program asks the user to select Fahrenheit or Celsius conversion
' and input a given temperature. Then the program converts the given 
' temperature and displays the result.
'
' References:
'     https://www.mathsisfun.com/temperature-conversion.html
'     https://en.wikibooks.org/wiki/BASIC_Programming

DECLARE SUB Main
DECLARE FUNCTION GetChoice$
DECLARE FUNCTION GetTemperature(Scale$)
DECLARE FUNCTION CalculateCelsius(Fahrenheit)
DECLARE FUNCTION CalculateFahrenheit(Celsius)
DECLARE SUB DisplayResult(Temperature, From$, Result, To$)

Main

SUB Main
    'Main could either be an If-Else structure or a Select-Case structure.

    DIM Choice$
    DIM Temperature
    DIM Result
    
    Choice$ = GetChoice$

    'If-Else approach
    IF Choice$ = "C" OR Choice$ = "c" THEN
        Temperature = GetTemperature("Fahrenheit")
        Result = CalculateCelsius(Temperature)
        DisplayResult Temperature, "Fahrenheit", Result, "Celsius"
    ELSE IF Choice$ = "F" OR Choice$ = "f" THEN
        Temperature = GetTemperature("Celsius")
        Result = CalculateFahrenheit(Temperature)
        DisplayResult Temperature, "Celsius", Result, "Fahrenheit"
    ELSE
        PRINT "You must enter C to convert to Celsius or F to convert to Fahrenheit!"
    END IF

    'Select-Case approach
    SELECT CASE Choice$
        CASE "C"
            Temperature = GetTemperature("Fahrenheit")
            Result = CalculateCelsius(Temperature)
            DisplayResult Temperature, "Fahrenheit", Result, "Celsius"
        CASE "c"
            Temperature = GetTemperature("Fahrenheit")
            Result = CalculateCelsius(Temperature)
            DisplayResult Temperature, "Fahrenheit", Result, "Celsius"
        CASE "F"
            Temperature = GetTemperature("Celsius")
            Result = CalculateFahrenheit(Temperature)
            DisplayResult Temperature, "Celsius", Result, "Fahrenheit"
        CASE "f"
            Temperature = GetTemperature("Celsius")
            Result = CalculateFahrenheit(Temperature)
            DisplayResult Temperature, "Celsius", Result, "Fahrenheit"
        CASE ELSE
            PRINT "You must enter C to convert to Celsius or F to convert to Fahrenheit!"
    END SELECT
END SUB

FUNCTION GetChoice$
    PRINT "Enter F to convert to Fahrenheit or C to convert to Celsius:"
    INPUT Choice$
    GetChoice$ = Choice$
END FUNCTION

FUNCTION GetTemperature(Label$)
    DIM Temperature
    
    PRINT "Enter " + Label$ + " temperature:"
    INPUT Temperature
        
    GetTemperature = Temperature
END FUNCTION

FUNCTION CalculateCelsius(Fahrenheit)
    DIM Celsius

    Celsius = (Fahrenheit - 32) * 5 / 9

    CalculateCelsius = Celsius
END FUNCTION

FUNCTION CalculateFahrenheit(Celsius)
    DIM Fahrenheit

    Fahrenheit = Celsius * 9 / 5 + 32

    CalculateFahrenheit = Fahrenheit
END FUNCTION

SUB DisplayResult(Temperature, FromLabel$, Result, ToLabel$)
    PRINT STR$(Temperature) + "° " + FromLabel$ + " is " + STR$(Result) + "° " + ToLabel$
END SUB
Try It

Copy and paste the code above into one of the following free online development environments or use your own BASIC compiler / interpreter / IDE.
repl.it
conditions.bas

Try It

See Also
