diff --git a/2021/puzzle-01-01.cc b/2021/puzzle-01-01.cc
index cdd7a0e..08a5149 100644
--- a/2021/puzzle-01-01.cc
+++ b/2021/puzzle-01-01.cc
@@ -7,9 +7,9 @@
 #include <limits>
 #include <string>
 
-int main(void)
+auto main() -> int
 {
-  unsigned long prev{std::numeric_limits<unsigned long>::max()};
+  auto prev{std::numeric_limits<std::uint64_t>::max()};
   unsigned incrs{0};
   std::string line;
   while (std::getline(std::cin, line)) {
diff --git a/2021/puzzle-01-02.cc b/2021/puzzle-01-02.cc
index 153df1a..4ad84ba 100644
--- a/2021/puzzle-01-02.cc
+++ b/2021/puzzle-01-02.cc
@@ -2,24 +2,25 @@
 // Created by Matthew Gretton-Dann on 01/12/2021.
 //
 
+#include <cassert>
 #include <cstdlib>
 #include <iostream>
 #include <limits>
 #include <string>
 #include <vector>
 
-int main(void)
+auto main() -> int
 {
-  std::vector<unsigned long> nums;
+  std::vector<std::uint64_t> nums;
   unsigned incrs{0};
   std::string line;
   while (std::getline(std::cin, line)) {
     nums.push_back(std::stoul(line));
   }
   assert(nums.size() >= 3);
-  unsigned long prev{std::numeric_limits<unsigned long>::max()};
+  std::uint64_t prev{std::numeric_limits<std::uint64_t>::max()};
   for (std::size_t pos = 0; pos <= nums.size() - 3; ++pos) {
-    unsigned long current{0};
+    std::uint64_t current{0};
     for (std::size_t i = pos + 0; i < pos + 3; ++i) {
       current += nums[i];
     }
diff --git a/2021/puzzle-02-01.cc b/2021/puzzle-02-01.cc
index f2212eb..49bec34 100644
--- a/2021/puzzle-02-01.cc
+++ b/2021/puzzle-02-01.cc
@@ -5,17 +5,17 @@
 #include <iostream>
 #include <string>
 
-int main()
+auto main() -> int
 {
   using namespace std::string_literals;
 
   static const auto fwd{"forward "s};
   static const auto down{"down "s};
-  static const auto up{"up "s};
+  static const auto up{"up "s}; // NOLINT(readability-identifier-length)
 
   std::string line;
-  unsigned long horiz{0};
-  unsigned long depth{0};
+  std::uint64_t horiz{0};
+  std::uint64_t depth{0};
   while (std::getline(std::cin, line)) {
     if (line.size() > fwd.size() && line.substr(0, fwd.size()) == fwd) {
       horiz += std::stoul(line.substr(fwd.size()));
diff --git a/2021/puzzle-02-02.cc b/2021/puzzle-02-02.cc
index 9a52283..8d6a4fc 100644
--- a/2021/puzzle-02-02.cc
+++ b/2021/puzzle-02-02.cc
@@ -5,18 +5,18 @@
 #include <iostream>
 #include <string>
 
-int main()
+auto main() -> int
 {
   using namespace std::string_literals;
 
   static const auto fwd{"forward "s};
   static const auto down{"down "s};
-  static const auto up{"up "s};
+  static const auto up{"up "s}; // NOLINT(readability-identifier-length)
 
   std::string line;
-  unsigned long horiz{0};
-  unsigned long depth{0};
-  unsigned long aim{0};
+  std::uint64_t horiz{0};
+  std::uint64_t depth{0};
+  std::uint64_t aim{0};
   while (std::getline(std::cin, line)) {
     if (line.size() > fwd.size() && line.substr(0, fwd.size()) == fwd) {
       auto dist{std::stoul(line.substr(fwd.size()))};