Updated the Variable object to reconize 'k' as an installment variable type. Updated the main program's interactive UI.

.gitignore

@@ -1,2 +1,3 @@
 __pycache__
 *.json
+*.txt

expression.py

@@ -19,7 +19,9 @@ class Variable:
 		"i" : "Interest",
 		"I" : "Interest",
 		"n" : "Time",
-		"N" : "Time"
+		"N" : "Time",
+		"k" : "Installment",
+		"K" : "Installment"
 	}
 	
 	def __init__(self, name, type, starting_point = 0, ending_point = 0):

main.py

@@ -8,9 +8,10 @@ import itertools
 import copy
 
 base_list = [1, 2, 4, 6, 12]
-tolerance = .28
+tolerance = .05
 
 variables = {}
+
 def print_vars(vars):
 	i = 0
 	for key in vars.keys():
@@ -74,10 +75,21 @@ def modify_variable(var, vars):
 			
 exp_str = input("Enter the expression the student will use: ")
 wrong_response = input("Enter the wrong response for the expression: ")
+
 try:
 	wrong_response = float(wrong_response)
 except ValueError:
-	print("The anwser must be numeric! Will not be included in output file.")
+	print("The wrong response must be numeric.")
+	exit()
+
+tolerance = input("Enter the tolerance to use: ")
+
+try:
+	tolerance = float(tolerance)
+except ValueError:
+	print("The tolerance must be numeric.")
+	exit()
+
 tokens = tokenizer.get_tokens_from_expression_string(exp_str)
 rev_tokens = copy.deepcopy(tokens)
 #rev_tokens.reverse()
@@ -88,6 +100,8 @@ for t in rev_tokens:
 
 selected_variable = None
 
+if len(variables) > 0:
+
 	while True:
 		print("Variables in expression:")
 		print_vars(variables)