diff --git a/include/type.hpp b/include/type.hpp
index 5e4f3299..5e76df45 100644
--- a/include/type.hpp
+++ b/include/type.hpp
@@ -176,9 +176,9 @@ class FuncType : public Type {
 
 class StructType : public Type {
  public:
-  /// @param id The identifier of a struct type.
-  explicit StructType(std::string id,
-                      std::vector<std::unique_ptr<Type>> field_types)
+  /// @param id The identifier of the struct type. May be empty ("") for unnamed
+  /// structs.
+  StructType(std::string id, std::vector<std::unique_ptr<Type>> field_types)
       : id_{std::move(id)}, field_types_{std::move(field_types)} {}
 
   bool IsStruct() const noexcept override {
@@ -197,9 +197,9 @@ class StructType : public Type {
 
 class UnionType : public Type {
  public:
-  /// @param id The identifier of a union type.
-  explicit UnionType(std::string id,
-                     std::vector<std::unique_ptr<Type>> field_types)
+  /// @param id The identifier of the union type. May be empty ("") for unnamed
+  /// unions.
+  UnionType(std::string id, std::vector<std::unique_ptr<Type>> field_types)
       : id_{std::move(id)}, field_types_{std::move(field_types)} {}
 
   bool IsUnion() const noexcept override {
diff --git a/lexer.l b/lexer.l
index 89d56d90..61cf7fad 100644
--- a/lexer.l
+++ b/lexer.l
@@ -48,7 +48,7 @@ integer [0-9]+
 ":" { return yy::parser::make_COLON(yylloc); }
 
 "," { return yy::parser::make_COMMA(yylloc); }
-"." { return yy::parser::make_PERIOD(yylloc); }
+"." { return yy::parser::make_DOT(yylloc); }
 
   /* operators */
 "-" { return yy::parser::make_MINUS(yylloc); }
diff --git a/parser.y b/parser.y
index a9bc2332..19a47ada 100644
--- a/parser.y
+++ b/parser.y
@@ -79,7 +79,7 @@ std::unique_ptr<Type> ResolveType(std::unique_ptr<Type> resolved_type,
 
 %token MINUS PLUS STAR DIV MOD ASSIGN
 %token EXCLAMATION TILDE AMPERSAND QUESTION
-%token COMMA PERIOD SEMICOLON COLON
+%token COMMA DOT SEMICOLON COLON
 // (), {}, []
 %token LEFT_PAREN RIGHT_PAREN LEFT_CURLY RIGHT_CURLY LEFT_SQUARE RIGHT_SQUARE
 
@@ -388,25 +388,24 @@ arg: expr {
 /* 6.7 Declarations */
 /* Declaration specifiers can be either a 'type' or a 'declaration of type'. */
 /* TODO: init declarator list */
-/* TODO: If the init declarator doesn't present, e.g., `int;`, the declaration is still valid. */
 decl: declaration_specifiers init_declarator_opt SEMICOLON {
     auto decl_specifers = $1;
     auto init_decl = $2;
     if (std::holds_alternative<std::unique_ptr<Type>>(decl_specifers)) {
       auto type = std::move(std::get<std::unique_ptr<Type>>(decl_specifers));
-      init_decl->type = ResolveType(std::move(type), std::move(init_decl->type));
+      if (init_decl) {
+        init_decl->type = ResolveType(std::move(type), std::move(init_decl->type));
+      } else { // unnamed primitive type
+        init_decl = std::make_unique<VarDeclNode>(Loc(@1), "", std::move(type));
+      }
+
       $$ = std::move(init_decl);
     } else {
       auto decl = std::move(std::get<std::unique_ptr<DeclNode>>(decl_specifers));
-      auto rec_decl = dynamic_cast<RecordDeclNode*>(decl.get());
+      auto* rec_decl = dynamic_cast<RecordDeclNode*>(decl.get());
       assert(rec_decl);
-      if (auto* rec_var_decl = dynamic_cast<RecordVarDeclNode*>(init_decl.get())) {
-        // A struct or union variable.
-        rec_var_decl->type = ResolveType(std::move(rec_decl->type), std::move(rec_var_decl->type));
-        decl = std::move(init_decl);
-      } else if (auto* arr_decl = dynamic_cast<ArrDeclNode*>(init_decl.get())) {
-        // An array with struct or union elements.
-        arr_decl->type = ResolveType(std::move(rec_decl->type), std::move(arr_decl->type));
+      if (init_decl) {
+        init_decl->type = ResolveType(std::move(rec_decl->type), std::move(init_decl->type));
         decl = std::move(init_decl);
       }
 
@@ -446,11 +445,10 @@ init_declarator: declarator { $$ = $1; }
         arr_decl->init_list = std::move(init_expr_list);
       } else if (auto* var_decl = dynamic_cast<VarDeclNode*>(decl.get())) {
         // Declares a struct or union variable.
-        auto rec_decl = std::make_unique<RecordVarDeclNode>(Loc(@1),
+        decl = std::make_unique<RecordVarDeclNode>(Loc(@1),
                                          std::move(var_decl->id),
                                          std::move(var_decl->type),
                                          std::move(init_expr_list));
-        decl = std::move(rec_decl);
       }
     }
     $$ = std::move(decl);
@@ -483,7 +481,7 @@ struct_or_union_specifier: struct_or_union id_opt LEFT_CURLY struct_declaration_
       type = std::make_unique<UnionType>(std::move(type_id), std::move(field_types));
     }
 
-    $$ = std::make_unique<RecordDeclNode>(Loc(@2), decl_id ? std::move(decl_id->id) : "", std::move(type), std::move(field_list));
+    $$ = std::make_unique<RecordDeclNode>(Loc(@2), std::move(type_id), std::move(type), std::move(field_list));
   }
   | struct_or_union ID {
     auto type = $1;
@@ -491,11 +489,10 @@ struct_or_union_specifier: struct_or_union id_opt LEFT_CURLY struct_declaration_
     auto field_list = std::vector<std::unique_ptr<FieldNode>>{};
     auto field_types = std::vector<std::unique_ptr<Type>>{};
 
-    auto type_id = decl_id;
     if (type->IsStruct()) {
-      type = std::make_unique<StructType>(std::move(type_id), std::move(field_types));
+      type = std::make_unique<StructType>(std::move(decl_id), std::move(field_types));
     } else {
-      type = std::make_unique<UnionType>(std::move(type_id), std::move(field_types));
+      type = std::make_unique<UnionType>(std::move(decl_id), std::move(field_types));
     }
 
     $$ = std::make_unique<RecordDeclNode>(Loc(@2), std::move(decl_id), std::move(type), std::move(field_list));
@@ -589,7 +586,7 @@ direct_declarator: ID {
     auto type = std::make_unique<ArrType>(std::move(declarator->type), $3);
     if (!dynamic_cast<ArrDeclNode*>(declarator.get())) {
       // If the declarator is not yet a array declarator, we need to construct one.
-      $$ = std::make_unique<ArrDeclNode>(Loc(@1), declarator->id, std::move(type), /* init list */ std::vector<std::unique_ptr<InitExprNode>>{});
+      $$ = std::make_unique<ArrDeclNode>(Loc(@1), declarator->id, std::move(type), std::vector<std::unique_ptr<InitExprNode>>{});
     } else {
       declarator->type = std::move(type);
       $$ = std::move(declarator);
@@ -709,7 +706,6 @@ direct_abstract_declarator_opt: direct_abstract_declarator { $$ = $1; }
   ;
 
 /* 6.7.8 Initialization */
-/* The current object shall have array type and the expression shall be an integer constant expression. */
 initializer: LEFT_CURLY initializer_list comma_opt RIGHT_CURLY { $$ = $2; }
   | assign_expr { $$ = std::make_unique<InitExprNode>(Loc(@1), std::vector<std::unique_ptr<DesNode>>{}, $1); }
   ;
@@ -743,10 +739,8 @@ designator_list: designator {
   }
   ;
 
-/* The current object shall have array type and the expression shall be an integer constant expression. */
 designator: LEFT_SQUARE const_expr RIGHT_SQUARE { $$ = std::make_unique<ArrDesNode>(Loc(@2), $2); }
-  /* The current object shall have structure or union type and the identifier shall be the name of a member of that type. */
-  | PERIOD ID { $$ = std::make_unique<IdDesNode>(Loc(@2), $2); }
+  | DOT ID { $$ = std::make_unique<IdDesNode>(Loc(@2), $2); }
   ;
 
 comma_opt: COMMA
diff --git a/src/type_checker.cpp b/src/type_checker.cpp
index 96f0dd2c..e321eaa7 100644
--- a/src/type_checker.cpp
+++ b/src/type_checker.cpp
@@ -356,11 +356,14 @@ void TypeChecker::Visit(InitExprNode& init_expr) {
 }
 
 void TypeChecker::Visit(ArrDesNode& arr_des) {
+  /* ArrDesNode shall have array type and the expression shall be an integer
+   * constant expression. */
   arr_des.index->Accept(*this);
 }
 
 void TypeChecker::Visit(IdDesNode& id_des) {
-  /* do nothing */
+  /* IdDesNode does nothing and shall have structure or union type and the
+   * identifier shall be the name of a member of that type. */
 }
 
 void TypeChecker::Visit(NullExprNode&) {
diff --git a/test/typecheck/decl.c b/test/typecheck/decl.c
index b0f92348..6fe845ec 100644
--- a/test/typecheck/decl.c
+++ b/test/typecheck/decl.c
@@ -1,4 +1,5 @@
 int main() {
   int i = 0;
   int j;
+  int;
 }
diff --git a/test/typecheck/decl.exp b/test/typecheck/decl.exp
index 55717e33..bcb3f0cd 100644
--- a/test/typecheck/decl.exp
+++ b/test/typecheck/decl.exp
@@ -4,3 +4,4 @@ ProgramNode <1:1>
       VarDeclNode <2:7> i: int
         IntConstExprNode <2:11> 0: int
       VarDeclNode <3:7> j: int
+      VarDeclNode <4:3> : int
diff --git a/test/typecheck/struct.c b/test/typecheck/struct.c
index 700dcdd5..730e598a 100644
--- a/test/typecheck/struct.c
+++ b/test/typecheck/struct.c
@@ -21,7 +21,7 @@ int main() {
 
   struct birth bd2 = {3, 3, 1998};
 
-  struct birth bd3[3] = { [0].date = 4, [1].year = 1999};
+  struct birth bd3[3] = {[0].date = 4, [1].year = 1999};
 
   return 0;
 }
diff --git a/test/typecheck/struct.exp b/test/typecheck/struct.exp
index d20fe9bb..ed1ce232 100644
--- a/test/typecheck/struct.exp
+++ b/test/typecheck/struct.exp
@@ -28,15 +28,15 @@ ProgramNode <1:1>
         InitExprNode <22:23>
           IntConstExprNode <22:29> 1998: int
       ArrDeclNode <24:16> bd3: struct birth[3]
-        InitExprNode <24:27>
-          ArrDesNode <24:28>
-            IntConstExprNode <24:28> 0: int
-          IdDesNode <24:31> date
-          IntConstExprNode <24:38> 4: int
-        InitExprNode <24:27>
-          ArrDesNode <24:42>
-            IntConstExprNode <24:42> 1: int
-          IdDesNode <24:45> year
-          IntConstExprNode <24:52> 1999: int
+        InitExprNode <24:26>
+          ArrDesNode <24:27>
+            IntConstExprNode <24:27> 0: int
+          IdDesNode <24:30> date
+          IntConstExprNode <24:37> 4: int
+        InitExprNode <24:26>
+          ArrDesNode <24:41>
+            IntConstExprNode <24:41> 1: int
+          IdDesNode <24:44> year
+          IntConstExprNode <24:51> 1999: int
       ReturnStmtNode <26:3>
         IntConstExprNode <26:10> 0: int
diff --git a/test/typecheck/union.c b/test/typecheck/union.c
index 8d9d0772..31138bfe 100644
--- a/test/typecheck/union.c
+++ b/test/typecheck/union.c
@@ -15,12 +15,12 @@ int main() {
     int e;
   };
 
-  // It's a legal case, but compiler will show warning of excessing elements.
+  // It's a legal case, but compilers like GCC may show warning of excessing elements.
   // The value of the members is 3.
   union shape s = {3, 4, 5};
   // Three members in circle variable share the same memory location, so every member is 1.
   union shape circle = {.circle = 1};
-  union shape puzzles[3] = { [0].circle = 1, [1].triangle = 2, [2].square = 4};
+  union shape puzzles[3] = {[0].circle = 1, [1].triangle = 2, [2].square = 4};
 
   return 0;
 }
diff --git a/test/typecheck/union.exp b/test/typecheck/union.exp
index 0caa1064..1720cbc6 100644
--- a/test/typecheck/union.exp
+++ b/test/typecheck/union.exp
@@ -24,20 +24,20 @@ ProgramNode <1:1>
           IdDesNode <22:26> circle
           IntConstExprNode <22:35> 1: int
       ArrDeclNode <23:15> puzzles: union shape[3]
-        InitExprNode <23:30>
-          ArrDesNode <23:31>
-            IntConstExprNode <23:31> 0: int
-          IdDesNode <23:34> circle
-          IntConstExprNode <23:43> 1: int
-        InitExprNode <23:30>
-          ArrDesNode <23:47>
-            IntConstExprNode <23:47> 1: int
-          IdDesNode <23:50> triangle
-          IntConstExprNode <23:61> 2: int
-        InitExprNode <23:30>
-          ArrDesNode <23:65>
-            IntConstExprNode <23:65> 2: int
-          IdDesNode <23:68> square
-          IntConstExprNode <23:77> 4: int
+        InitExprNode <23:29>
+          ArrDesNode <23:30>
+            IntConstExprNode <23:30> 0: int
+          IdDesNode <23:33> circle
+          IntConstExprNode <23:42> 1: int
+        InitExprNode <23:29>
+          ArrDesNode <23:46>
+            IntConstExprNode <23:46> 1: int
+          IdDesNode <23:49> triangle
+          IntConstExprNode <23:60> 2: int
+        InitExprNode <23:29>
+          ArrDesNode <23:64>
+            IntConstExprNode <23:64> 2: int
+          IdDesNode <23:67> square
+          IntConstExprNode <23:76> 4: int
       ReturnStmtNode <25:3>
         IntConstExprNode <25:10> 0: int