Fixed a bug where addition would always be evaluated before subtraction when, in reality, they have the same precedence.

calculator.py

@@ -90,14 +90,15 @@ def evaluate(subexpr): # Evaluate a tokenized expression, that contains no paran
 		subexpr[index] = float(subexpr[index-1]) * float(subexpr[index+1])
 		subexpr[index-1] = ''
 		subexpr[index+1] = ''
-	elif '+' in subexpr:
-		index = subexpr.index('+')
-		subexpr[index] = float(subexpr[index-1]) + float(subexpr[index+1])
-		subexpr[index-1] = ''
-		subexpr[index+1] = ''
-	elif '-' in subexpr:
-		index = subexpr.index('-')
-		subexpr[index] = float(subexpr[index-1]) - float(subexpr[index+1])
+	elif '+' in subexpr or '-' in subexpr: # Addition and subtraction have the same precedence
+		index_plus, index_minus = float('inf'), float('inf') # Set both values to infinity
+		if '+' in subexpr:
+			index_plus = subexpr.index('+')
+		if '-' in subexpr:
+			index_minus = subexpr.index('-')
+
+		index = index_plus if index_plus < index_minus else index_minus # Set the index to the index of the operator that occurs first
+		subexpr[index] = float(subexpr[index-1]) + float(subexpr[index+1]) if index_plus < index_minus else float(subexpr[index-1]) - float(subexpr[index+1]) # If addition occured first, add the previous and next tokens. If subtraction occured first, subtract them.
 		subexpr[index-1] = ''
 		subexpr[index+1] = ''