If statement for pythagorean function where "c" has to be greater than "a" or "b"

Question

I am building a function in r that takes 2 arguments and computes the missing side of a triangle using the pythagorean theorem. I have made it so that stop messages appear if certain criteria are not met. For example, the first stop message checks whether the arguments are numeric. My trouble here is getting the message to appear if the argument c is less than a or b. When c=a or c=b the output is 0. When c<a or c<b the output is NaN. Other than that, it works just fine. I have messed around with that chunk of code and am stuck. Any suggestions?

pythagorean <- function( a = NULL, b = NULL, c = NULL){
sides <- c(a, b, c)                              

#stop message will appear if arguments are not numeric
if(!is.numeric(sides)){                         
  stop("Arguments must be numeric")
}


#stop message will appear if the amount of arguments is not 2 
if(length(sides) <2){                           
  stop("Must provide 2 arguments")
}else if(length(sides) >2){                    
  stop("Must provide 2 arguments")
}


#if a or b are greater than or equal c, it will not be calculated
#otherwise, the missing value will be calculated
if(!is.null(b) & !is.null(a) >= !is.null(c)){                           
  stop("c must be greater than a")
}else if(!is.null(a) & !is.null(b) >= !is.null(c)){                           
  stop("c must be greater than b")
}else

  #calculate c if a and b are given
  if(is.null(c)){   
    sqrt(a^2 + b^2)
  
  #calculate b if a and c are given
  }else if (is.null(a)){    
    sqrt((c^2) - (b^2))
  
  #calculate a if b and c are given
  }else if (is.null(b)){   
    sqrt((c^2) - (a^2))
  }
}

#samples testing the code
pythagorean(a=5, c=5) #c=a
pythagorean(b=3, c=3) #c=b
pythagorean(a=8, c=4) #c<b
pythagorean(a=9, c=6) #c<a
pythagorean(a=5, c=10) #c>a
pythagorean(b=3, c=12) #c>b
pythagorean(a=3, b=4) #calculating for c
pythagorean(b=4, c=5) #calculating for a
pythagorean(a=3, c=5) #calculating for b
pythagorean(a=-3, c=5) #takes negative numbers

#output
[1] 0
[1] 0
NaNs produced[1] NaN
NaNs produced[1] NaN
[1] 8.660254
[1] 11.61895
[1] 5
[1] 3
[1] 4
[1] 4

Answer 1

Using scalar operator (&&) will be helpful here.

 #...
 if(!is.null(a) && !is.null(c) && c <= a){                           
    stop("c must be greater than a")
  }else if(!is.null(b) && !is.null(c) && c <= b){                           
    stop("c must be greater than b")
  }else
 #...
 #...

pythagorean(a=5, c=5) #c=a
#Error in pythagorean(a = 5, c = 5) : c must be greater than a
pythagorean(b=3, c=3) #c=b
#Error in pythagorean(b = 3, c = 3) : c must be greater than b
pythagorean(a=8, c=4) #c<b
#Error in pythagorean(a = 8, c = 4) : c must be greater than a
pythagorean(a=9, c=6) #c<a
#Error in pythagorean(a = 9, c = 6) : c must be greater than a
pythagorean(a=5, c=10) #c>a
#[1] 8.660254
pythagorean(b=3, c=12) #c>b
#[1] 11.61895
pythagorean(a=3, b=4) #calculating for c
#[1] 5
pythagorean(b=4, c=5) #calculating for a
#[1] 3
pythagorean(a=3, c=5) #calculating for b
#[1] 4
pythagorean(a=-3, c=5) #takes negative numbers
#[1] 4