Updated TODO

README.md

@@ -20,5 +20,5 @@ The reason I chose to do this, is that my parsing algorithm considers everything
 - Simple error checking
 
 ## To-do
-- Simple algebraic parsing (assign values to variables, etc.)
+- ~~Simple algebraic parsing (assign values to variables, etc.)~~
 - More robust error-checking

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()

parse.py

@@ -1,6 +1,6 @@
 def parse(expr):
 
-	opers = ['+', '-', '*', '/']
+	opers = ['+', '-', '*', '/', '=']
 
 	num_par = 0
 	tokenized = []
@@ -9,19 +9,19 @@ def parse(expr):
 	while index < len(expr):
 		if expr[index] in opers:
 			tokenized.append(expr[index])
+			index += 1
 
 		elif expr[index].isdigit() or expr[index] == '.':
 			while (index < len(expr)) and (expr[index].isdigit() or expr[index] == '.'):
 				temp_string += expr[index]
 				index += 1
 			tokenized.append(temp_string)
-			temp_string = ""
 
 		elif expr[index] == '(':
 			num_par = 1
 			temp_string += expr[index]
 			index += 1
-			while num_par != 0 and index < len(expr):
+			while index < len(expr) and num_par != 0:
 				temp_string += expr[index]
 				if expr[index] == '(':
 					num_par += 1
@@ -30,9 +30,18 @@ def parse(expr):
 				index += 1
 
 			tokenized.append(temp_string)
-			temp_string = ""
 
+		elif expr[index].isalpha(): # If you encounter a variable
+			temp_string += expr[index]
+			index += 1
+			while index < len(expr) and expr[index].isalpha():
+				temp_string += expr[index]
+				index += 1
+			tokenized.append(temp_string)
 
-		index += 1
+		else:
+			index += 1
+
+		temp_string = ""
 
 	return tokenized

todo.txt

@@ -1,3 +1,3 @@
-1. Implement variable assignment e.g. x = 5
-2. ALlow these variables to be used in future expressions
+----DONE---- 1. Implement variable assignment e.g. x = 5
+----DONE---- 2. Allow these variables to be used in future expressions
 3. Implement additional error-checking