diff --git a/day1/examples/fibonacci.cc b/day1/examples/fibonacci.cc
new file mode 100644
index 0000000000000000000000000000000000000000..61f74e0399524b841184fa0042185cf7c4606740
--- /dev/null
+++ b/day1/examples/fibonacci.cc
@@ -0,0 +1,12 @@
+#include <iostream>
+#include <limits>
+
+int main()
+{
+ size_t umax{ std::numeric_limits<size_t>::max() };
+ unsigned nfib = 0;
+ size_t f0{ 0 }, f1{ 1 };
+ // Insert your code here
+ std::cout << "The largest number in the Fibonacci sequence under " << umax << " is " << f1 << "\n";
+ std::cout << "Number of entries in the Fibonacci sequence under " << umax << " is " << nfib << "\n";
+}
diff --git a/day1/examples/gcd.cc b/day1/examples/gcd.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b355e66f122f6c5b99810caef43de9061f991d3b
--- /dev/null
+++ b/day1/examples/gcd.cc
@@ -0,0 +1,21 @@
+#include <iostream>
+
+unsigned long euclid_gcd(unsigned long smaller, unsigned long larger)
+{
+ if (smaller > larger)
+ std::swap(smaller, larger);
+ // Fill in your code to implement Euclid's algorithm here.
+
+ return ? ? ? ;
+}
+
+int main(int argc, char* argv[])
+{
+ if (argc != 3) {
+ std::cout << "Usage:\n"
+ << argv[0] << " number1 number2\n";
+ return 1;
+ }
+ unsigned long n1 = std::stoul(argv[1]), n2 = std::stoul(argv[2]);
+ std::cout << euclid_gcd(n1, n2) << "\n";
+}
diff --git a/day1/examples/hanoi.cc b/day1/examples/hanoi.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3f457bd1957988c7100946328dcb74e5e53c97cc
--- /dev/null
+++ b/day1/examples/hanoi.cc
@@ -0,0 +1,19 @@
+#include <iostream>
+#include <string>
+int the_other(int i, int j) { return 3 - i - j; }
+
+void transfer(unsigned long n, int from, int to)
+{
+ int oth = the_other(from, to);
+ if (n > 1)
+ transfer(n - 1, from, oth);
+ std::cout << n << ": " << from << "->" << to << "\n";
+ if (n > 1)
+ transfer(n - 1, oth, to);
+}
+
+int main()
+{
+ size_t N = 6;
+ transfer(N, 0, 1);
+}
diff --git a/day1/examples/hello_qa.cc b/day1/examples/hello_qa.cc
new file mode 100644
index 0000000000000000000000000000000000000000..55fd5b28327407c534c69b9d29fa7713a248772f
--- /dev/null
+++ b/day1/examples/hello_qa.cc
@@ -0,0 +1,12 @@
+// examples/hello_qa.cc
+#include <string>
+#include <iostream>
+
+int main()
+{
+ std::string name;
+ std::cout << "What's your name ? ";
+ std::cin >> name;
+ std::cout << "Hello, " << name << "\n";
+}
+
diff --git a/day1/examples/hello_xyz.cc b/day1/examples/hello_xyz.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b75bb497765a0e4bb3416e3ce21170dc63544215
--- /dev/null
+++ b/day1/examples/hello_xyz.cc
@@ -0,0 +1,10 @@
+// examples/hello_xyz.cc
+#include <iostream>
+auto main(int argc, char* argv[]) -> int
+{
+ std::cout << "Hello, ";
+ if (argc > 1)
+ std::cout << argv[1] << "!\n";
+ else
+ std::cout << "world!\n";
+}
diff --git a/day1/examples/namespaces.cc b/day1/examples/namespaces.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8d908bd2ad73747a24d1e46b165d1ff701bbfded
--- /dev/null
+++ b/day1/examples/namespaces.cc
@@ -0,0 +1,17 @@
+#include <iostream>
+
+using namespace std;
+
+namespace UnitedKingdom {
+string London = "Big city";
+}
+namespace UnitedStates {
+string London = "Small town in Kentucky";
+}
+int main()
+{
+ using namespace UnitedKingdom;
+ cout << London << endl;
+ cout << UnitedStates::London << endl;
+ return 0;
+}
\ No newline at end of file
diff --git a/day1/examples/namespaces2.cc b/day1/examples/namespaces2.cc
new file mode 100644
index 0000000000000000000000000000000000000000..481dbf2d185b3835b66183eab1f82ba0ee377a7b
--- /dev/null
+++ b/day1/examples/namespaces2.cc
@@ -0,0 +1,22 @@
+#include <iostream>
+namespace UnitedKingdom {
+std::string London = "Big city";
+}
+namespace UnitedStates {
+namespace KY {
+ std::string London = "Small town in Kentucky";
+}
+namespace OH {
+ std::string London = "Small town in Ohio";
+}
+}
+// The following definition is ok in C++17
+//namespace mylibrary::onefeature {
+// double solve(int i);
+//}
+int main()
+{
+ namespace USOH = UnitedStates::OH;
+ std::cout << USOH::London << std::endl;
+ return 0;
+}
diff --git a/day1/examples/numsort.cc b/day1/examples/numsort.cc
new file mode 100644
index 0000000000000000000000000000000000000000..90589b393a19c64bc64764a07a4fbc3a5dab7a91
--- /dev/null
+++ b/day1/examples/numsort.cc
@@ -0,0 +1,40 @@
+#include <iostream>
+#include <string>
+#include <fstream>
+#include <filesystem>
+#include <vector>
+#include <sstream>
+
+namespace fs = std::filesystem;
+auto as_lines(fs::path file) -> std::vector<std::string>
+{
+ std::ifstream fin{ file };
+ std::string line;
+ std::vector<std::string> lines;
+ while (getline(fin, line)) lines.push_back(line);
+ return lines;
+}
+
+auto main(int argc, char* argv[]) -> int
+{
+ if (argc != 2) {
+ std::cerr << "Usage:\n"
+ << argv[0] << " filename\n";
+ return 1;
+ }
+ auto content = as_lines(argv[1]);
+ std::sort(content.begin(), content.end(),
+ [](auto l1, auto l2) {
+ std::istringstream istr1{ l1 };
+ std::istringstream istr2{ l2 };
+ auto x1{0.}, x2{0.};
+ istr1 >> x1;
+ istr2 >> x2;
+ return x1 < x2;
+ }
+ );
+ for (std::string_view line : content) {
+ std::cout << line << "\n";
+ }
+}
+
diff --git a/day1/examples/onespace.cc b/day1/examples/onespace.cc
new file mode 100644
index 0000000000000000000000000000000000000000..8b1037a9b6ea80f37411ae0ec4146aa917b80ae9
--- /dev/null
+++ b/day1/examples/onespace.cc
@@ -0,0 +1,24 @@
+// examples/onespace.cc
+#include <iostream>
+
+auto main(int argc, char* argv[]) -> int
+{
+ std::string line;
+ while (getline(std::cin, line)) {
+ if (line.empty()) {
+ continue;
+ }
+ bool sp{true};
+ for (auto c : line) {
+ if (isspace(c)) {
+ if (not sp) std::cout << '\t';
+ sp = true;
+ } else {
+ sp = false;
+ std::cout << c;
+ }
+ }
+ std::cout << "\n";
+ }
+}
+
diff --git a/day1/examples/raw1.cc b/day1/examples/raw1.cc
new file mode 100644
index 0000000000000000000000000000000000000000..0781800a602f8463ce7eba4483e5bf99ccb6738a
--- /dev/null
+++ b/day1/examples/raw1.cc
@@ -0,0 +1,8 @@
+#include <iostream>
+#include <string>
+
+int main()
+{
+ std::cout << "Use a single backslash character at the end of the line to continue input to the next line, as shown ...\n"
+ << "OBJ=a.o \\\n\tb.o\\\n\tc.o\n";
+}
diff --git a/day1/examples/rawstring.cc b/day1/examples/rawstring.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2c57d2dce8aa6781bc8fd2e48e75663bc6b1e1f7
--- /dev/null
+++ b/day1/examples/rawstring.cc
@@ -0,0 +1,14 @@
+#include <iostream>
+#include <string>
+
+int main()
+{
+ // clang-format off
+ std::string s = R"xyz(This is a " raw " C++11 string.)xyz";
+ std::cout << s << '\n';
+ s = R"(Inside a raw string \n does not create a new line.)";
+ std::cout << s << '\n';
+ s = R"(The regular expression to match a sequence of up to 3 digits is \d{3})";
+ // clang-format on
+ std::cout << s << '\n';
+}
diff --git a/day1/solutions/fibonacci.cc b/day1/solutions/fibonacci.cc
new file mode 100644
index 0000000000000000000000000000000000000000..fc9cf9685fbaa2754eb2a1bae15540c32771583f
--- /dev/null
+++ b/day1/solutions/fibonacci.cc
@@ -0,0 +1,17 @@
+#include <iostream>
+#include <limits>
+
+auto main() -> int
+{
+ size_t umax{ std::numeric_limits<size_t>::max() };
+ unsigned nfib = 0;
+ size_t f0{ 0 }, f1{ 1 };
+ do {
+ size_t f2 = f0 + f1;
+ f0 = f1;
+ f1 = f2;
+ ++nfib;
+ } while (f1 < umax - f0);
+ std::cout << "The largest number in the Fibonacci sequence under " << umax << " is " << f1 << "\n";
+ std::cout << "Number of entries in the Fibonacci sequence under " << umax << " is " << nfib << "\n";
+}
diff --git a/day1/solutions/gcd.cc b/day1/solutions/gcd.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f545c4eb5e609e30241a8d930780b8178a5b212e
--- /dev/null
+++ b/day1/solutions/gcd.cc
@@ -0,0 +1,24 @@
+#include <iostream>
+
+auto euclid_gcd(unsigned long smaller, unsigned long larger) -> unsigned long
+{
+ if (smaller > larger)
+ std::swap(smaller, larger);
+ while (smaller != 0) {
+ auto rem = larger % smaller;
+ larger = smaller;
+ smaller = rem;
+ }
+ return larger;
+}
+
+auto main(int argc, char* argv[]) -> int
+{
+ if (argc != 3) {
+ std::cout << "Usage:\n"
+ << argv[0] << " number1 number2\n";
+ return 1;
+ }
+ unsigned long n1 = std::stoul(argv[1]), n2 = std::stoul(argv[2]);
+ std::cout << euclid_gcd(n1, n2) << "\n";
+}
diff --git a/day1/solutions/raw1.cc b/day1/solutions/raw1.cc
new file mode 100644
index 0000000000000000000000000000000000000000..abe15584291f9d73737da98823bfe7fdf184dc56
--- /dev/null
+++ b/day1/solutions/raw1.cc
@@ -0,0 +1,12 @@
+#include <iostream>
+#include <string>
+
+auto main() -> int
+{
+ using namespace std;
+ cout << "Use a single backslash character at the end of the line to continue input to the next line, as shown ...\n"
+ << R"(OBJ=a.o \
+ b.o\
+ c.o
+)";
+}