diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..cb5b410
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,19 @@
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/*.code-snippets
+
+# Local History for Visual Studio Code
+.history/
+
+# Built Visual Studio Code Extensions
+*.vsix
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.history
+.ionide
+.clang-format
\ No newline at end of file
diff --git a/src/bin_search.py b/src/bin_search.py
index 713abfc..1d677f0 100644
--- a/src/bin_search.py
+++ b/src/bin_search.py
@@ -1,6 +1,8 @@
 def binSearch(xs: list[int], x: int):
     left, right = 0, len(xs) - 1
-    while left < right:
+    if not isinstance(x, int):
+        raise TypeError(f'X must be int, but {type(x)}')
+    while left <= right:
         mid = (left + right) // 2
         if xs[mid] == x:
             return mid
diff --git a/src/checksum.py b/src/checksum.py
index 74b4fb0..35bfeb6 100644
--- a/src/checksum.py
+++ b/src/checksum.py
@@ -1,14 +1,28 @@
 def modulo11Checksum(ISBNNumber: str):
-
     digits = [int(char) for char in ISBNNumber if char.isdigit()]
-
-    checkDigit = digits[-1]
-
+    if ISBNNumber[-1] == 'x' or ISBNNumber[-1] == 'X':
+        digits += [10]
     total = 0
-    for i in range(len(digits) - 1):
-        weight = 10
+    if len(digits) != 10:
+        print("incorrect input, should be 10 numbers")
+        return False
+    for i in range(10):
+        weight = 10 - i
         digit = digits[i]
         total += digit * weight
+    if total % 11 == 0:
+        print("correct")
+        return True
+    else:
+        print("incorrect")
+        return False
+
+isbnnum = input('input your number: ')
+while isbnnum != '-1':
+    modulo11Checksum(isbnnum)
+    isbnnum = input('input your number: ')
+
+
+
+
 
-    checksum = total + checkDigit
-    return checksum % 11 == 0
diff --git a/test/test_checksum.py b/test/test_checksum.py
index f64a64c..d41e053 100644
--- a/test/test_checksum.py
+++ b/test/test_checksum.py
@@ -2,8 +2,12 @@
 
 
 def test_good():
-    assert modulo11Checksum("2-266-11156-8")
+    assert modulo11Checksum("2-266-11156-6")
 
 
 def test_bad():
     assert not modulo11Checksum("2-266-11156-3")
+    
+def test_with_x():
+    assert modulo11Checksum("156-881-111-x")
+