diff --git a/calculator.py b/calculator.py
index e7131e8..3b23c9f 100644
--- a/calculator.py
+++ b/calculator.py
@@ -2,10 +2,12 @@ import re
 from parse import *
 
 # List of valid operators
-opers = ['+', '-', '*', '/']
+opers = ['+', '-', '*', '/', '=']
 
 # Regular expression that checks for valid characters in an expression
-valid_chars = '[ 0-9.\(\)+-\/*]'
+valid_chars = '[ 0-9a-z.\(\)+-\/*=]'
+
+variables = {}
 
 def print_error(error_code):
 
@@ -24,6 +26,8 @@ def print_error(error_code):
 			print("You have two operators next to each other.")
 		case 4:
 			print("One of your values is improperly formatted.")
+		case 5:
+			print("Uninitialized variable.")
 	
 def check_errors(expr):
 	expr_small = expr.replace(" ", "") # Remove spaces from the string, to make it easier to parse
@@ -54,9 +58,10 @@ def check_errors(expr):
 
 	expr = parse(expr)
 	for val in expr:
-		if val.count('.') > 1:
+		if val.count('.') > 1:  # A value can have at most 1 period
 			return 4
-
+		if val.isalpha() and not val in variables and val != expr[0]: # If the token is a string, and isn't in the dictionary, and isn't the variable at index 0 (e.g. 'x' in 'x = 4')
+			return 5
 	return 0
 		
 
@@ -66,6 +71,12 @@ def evaluate(subexpr): # Evaluate a tokenized expression, that contains no paran
 
 	print(subexpr)
 
+	for index, val in enumerate(subexpr): # Replace variables with their values
+		if str(val).isalpha():
+			subexpr[index] = variables[val]
+	
+	print(subexpr)
+
 	if (len(subexpr) == 1):
 		return float(subexpr[0])
 
@@ -113,12 +124,28 @@ def find_inner(subexpr):
 
 def main():
 	while True:
+		variable = ''
 		expr = input()
 		errno = check_errors(expr)
 		if errno != 0:
 			print_error(errno)
 			continue # If an error was generated, print an error message and continue on to the next iteration of the loop
-		expr = find_inner(expr)
+
+		expr_tokenized = parse(expr)
+
+		if expr_tokenized[0].isalpha() and expr_tokenized[1] == '=': # If the expression assigns a value to a variable
+			variable = expr_tokenized[0] # The first token is the variable
+
+			expr_tokenized.pop(0) # Remove the first and second tokens
+			expr_tokenized.pop(0)
+
+			expr = find_inner(''.join(expr_tokenized))
+			variables.update({variable: expr})
+
+		else:
+			expr = find_inner(expr)
+
 		print(expr)
+		print(variables)
 
 main()