From 1bbc7174c7360c408f01b6f6da8c47b77d394f07 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Sun, 26 Nov 2023 11:12:48 -0500
Subject: [PATCH] Added additional error-checking

---
 calculator.py | 44 ++++++++++++++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/calculator.py b/calculator.py
index c84afea..e224e9d 100644
--- a/calculator.py
+++ b/calculator.py
@@ -1,34 +1,47 @@
 import re
 from parse import *
 
+# List of valid operators
+opers = ['+', '-', '*', '/']
+
 # Regular expression that checks for valid characters in an expression
-valid_chars = '[0-9.\(\)+-\/*]'
+valid_chars = '[ 0-9.\(\)+-\/*]'
 
-def raise_error(error_code):
+def print_error(error_code):
 
 	# List of error codes:
-	# 0 - Invalid characters found in expression
-	# 1 - Unclosed parantheses
+	# 1 - Invalid characters found in expression
+	# 2 - Unclosed parantheses
 
 	match error_code:
-		case 0:
-			print("You have invalid characters in your expression.")
 		case 1:
+			print("You have invalid characters in your expression.")
+		case 2:
 			print("You have an unclosed parantheses in your expression.")
+		case 3:
+			print("You have two operators next to each other.")
 	
-	main() # Re-enter main loop
-
 def check_errors(expr):
 	# Check if number of opening parantheses is equal to number of closing parantheses
 	num_open_pars = 0
 	num_close_pars = 0
 	for val in expr:
-		num_open_pars += 1 if val == '('
-		num_close_pars += 1 if val == ')'
-		if num_open_pars != num_close_pars:
-			raise_error(2) 
-		
+		if not re.match(valid_chars, val):
+			return 1
 
+		num_open_pars = num_open_pars+1 if val == '(' else num_open_pars 
+		num_close_pars = num_close_pars+1 if val == ')' else num_close_pars
+
+		if val in opers:
+			#Check if the next element is an operator. If it is, throw an error
+			continue
+
+	if num_open_pars != num_close_pars:
+		return 2
+
+
+	return 0
+		
 
 def evaluate(subexpr): # Evaluate a tokenized expression, that contains no parantheses
 
@@ -84,7 +97,10 @@ def find_inner(subexpr):
 def main():
 	while True:
 		expr = input()
-		check_for_errors(expr)
+		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)
 		print(expr)