diff --git a/.idea/.gitignore b/.idea/.gitignore
new file mode 100644
index 0000000..26d3352
--- /dev/null
+++ b/.idea/.gitignore
@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml
diff --git a/.idea/.name b/.idea/.name
new file mode 100644
index 0000000..8701cdf
--- /dev/null
+++ b/.idea/.name
@@ -0,0 +1 @@
+4.21.py
\ No newline at end of file
diff --git a/.idea/inspectionProfiles/profiles_settings.xml b/.idea/inspectionProfiles/profiles_settings.xml
new file mode 100644
index 0000000..105ce2d
--- /dev/null
+++ b/.idea/inspectionProfiles/profiles_settings.xml
@@ -0,0 +1,6 @@
+<component name="InspectionProjectProfileManager">
+  <settings>
+    <option name="USE_PROJECT_PROFILE" value="false" />
+    <version value="1.0" />
+  </settings>
+</component>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 0000000..d1e22ec
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.8" project-jdk-type="Python SDK" />
+</project>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
new file mode 100644
index 0000000..211bc2e
--- /dev/null
+++ b/.idea/modules.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/task-3-2-1-Text-Processing-Introduction.iml" filepath="$PROJECT_DIR$/.idea/task-3-2-1-Text-Processing-Introduction.iml" />
+    </modules>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/task-3-2-1-Text-Processing-Introduction.iml b/.idea/task-3-2-1-Text-Processing-Introduction.iml
new file mode 100644
index 0000000..d0876a7
--- /dev/null
+++ b/.idea/task-3-2-1-Text-Processing-Introduction.iml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="PYTHON_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$" />
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..35eb1dd
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/4.21.py b/4.21.py
new file mode 100644
index 0000000..bb42881
--- /dev/null
+++ b/4.21.py
@@ -0,0 +1,35 @@
+s = "Hello"
+print("1. 字符 ASCII 码:")
+for ch in s:
+    print(f"  '{ch}' -> {ord(ch)}")
+
+
+print("\n2. 验证 chr(65):")
+print(f"  chr(65) = '{chr(65)}'")
+
+
+A = [3, 4]
+B = [1, 2]
+
+
+
+def add_vectors(v1, v2):
+    return [v1[0] + v2[0], v1[1] + v2[1]]
+
+
+
+def scalar_multiply(scalar, v):
+    return [scalar * v[0], scalar * v[1]]
+
+
+
+import math
+def vector_length(v):
+    return math.sqrt(v[0]**2 + v[1]**2)
+
+print("\n3. 向量计算:")
+print(f"  A = {A}")
+print(f"  B = {B}")
+print(f"  A + B = {add_vectors(A, B)}")
+print(f"  2 × A = {scalar_multiply(2, A)}")
+print(f"  A 的模 = {vector_length(A)}")
\ No newline at end of file