## ----function-farKelv-----------------------------------------------------------------
fahr_to_kelvin <- function(temp) {
	kelvin <- ((temp - 32) * (5/9)) + 273.15
	kelvin
}



## ----function-format, eval=FALSE------------------------------------------------------
## 
## FunctionNameHere <- function(Input-variable-here){
## 	what-to-do-here
## 	what-to-return-here
## }
## 


## ----call-function--------------------------------------------------------------------
# call function for F=32 degrees
fahr_to_kelvin(32)

# We could use `paste()` to create a sentence with the answer
paste('The boiling point of water (212 Fahrenheit) is', 
      fahr_to_kelvin(212),
      'degrees Kelvin.')


## ----funct-test-----------------------------------------------------------------------
fahr_to_kelvin_test <- function(temp) {
	kelvin <- ((temp - 32) * (5 / 9)) + 273.15
}



## ----funct-test-2---------------------------------------------------------------------

fahr_to_kelvin_test(32)



## ----funct-test-3---------------------------------------------------------------------
# assign to a
a <- fahr_to_kelvin_test(32)

# value of a
a


## ----scope----------------------------------------------------------------------------
x <- 1:3
x

# define a function to add 1 to the temporary variable 'input'
plus_one <- function(input) {
  input <- input + 1
}

# run our function
plus_one(x)

# x has not actually changed outside of the function
x


## ----scope-2--------------------------------------------------------------------------
plus_one <- function(input) {
  output <- input + 1     # store results to output variable
  output                  # return output variable
}

# assign the results of our function to x
x <- plus_one(x)
x



## ----challenge-code-kelv-to-cels, include=TRUE, results="hide", echo=FALSE------------

kelvin_to_celsius <- function(temp) {
	Celsius <- temp - 273.15
	Celsius
}
	
paste('absolute zero (0 Kelvin) in Celsius:', kelvin_to_celsius(0))
	


## ----compound-function----------------------------------------------------------------

# use two functions (F->K & K->C) to create a new one (F->C)
fahr_to_celsius <- function(temp) {
	temp_k <- fahr_to_kelvin(temp)
	temp_c <- kelvin_to_celsius(temp_k)
	temp_c
}
	
paste('freezing point of water (32 Fahrenheit) in Celsius:', 
      fahr_to_celsius(32.0))