diff --git a/day1/solutions/CMakeLists.txt b/day1/solutions/CMakeLists.txt
new file mode 100644
index 0000000000000000000000000000000000000000..b2fb1111d7944a0dbcca85cceea068b349b85661
--- /dev/null
+++ b/day1/solutions/CMakeLists.txt
@@ -0,0 +1,15 @@
+cmake_minimum_required(VERSION 3.16)
+set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+project(cxx2023_d1_solutions CXX)
+
+
+FILE (GLOB sources ./ *.cc)
+foreach(source ${sources})
+ get_filename_component(withoutext "${source}" NAME_WE)
+ add_executable("${withoutext}" "${source}")
+endforeach()
+
+
diff --git a/day1/solutions/check_prime.cc b/day1/solutions/check_prime.cc
new file mode 100644
index 0000000000000000000000000000000000000000..de7bfc26c72ee14c5e65694690ae33cbb1cbf484
--- /dev/null
+++ b/day1/solutions/check_prime.cc
@@ -0,0 +1,25 @@
+#include <iostream>
+
+auto is_prime(unsigned int n) -> bool
+{
+ bool found_divisor = false;
+ for (auto i = 2U;
+ (not found_divisor) and i * i <= n;
+ ++i) {
+ if (n % i == 0U) found_divisor = true;
+ }
+ return (not found_divisor);
+}
+
+auto main() -> int
+{
+ std::cout << "Number to check: ";
+ unsigned int inp{};
+ std::cin >> inp;
+ if (is_prime(inp))
+ std::cout << "Yes, that's a prime.\n";
+ else
+ std::cout << "Not a prime.\n";
+}
+
+
diff --git a/day1/solutions/fibonacci.cc b/day1/solutions/fibonacci.cc
new file mode 100644
index 0000000000000000000000000000000000000000..307d6ac7fd97ff674e1c3832fb3670985bec2535
--- /dev/null
+++ b/day1/solutions/fibonacci.cc
@@ -0,0 +1,33 @@
+#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";
+}
+#include <iostream>
+#include <limits>
+#include <format>
+
+auto main() -> int
+{
+ using namespace std;
+ size_t umax{ numeric_limits<size_t>::max() };
+ unsigned nfib = 0;
+ size_t f0{ 0 }, f1{ 1 };
+ // Insert your code here
+
+ cout << format(R"(The largest number in the Fibonacci sequence under {0:} is {1:},
+and there are {2:} entries under {0:} in that sequence.
+)" , umax, f1, nfib);
+}
diff --git a/day1/solutions/gcd.cc b/day1/solutions/gcd.cc
new file mode 100644
index 0000000000000000000000000000000000000000..153b3e41ef77ebadbcca7cc23a2026bc861f9943
--- /dev/null
+++ b/day1/solutions/gcd.cc
@@ -0,0 +1,45 @@
+#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";
+}
+#include <iostream>
+
+auto euclid_gcd(unsigned long smaller, unsigned long larger) -> unsigned long
+{
+ if (smaller > larger)
+ std::swap(smaller, larger);
+ // Fill in your code to implement Euclid's algorithm here.
+
+ return ? ? ? ;
+}
+
+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/midpt.cc b/day1/solutions/midpt.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b5b420c27733e045e1f66aad48a2d1125e4dc911
--- /dev/null
+++ b/day1/solutions/midpt.cc
@@ -0,0 +1,16 @@
+// examples/midpt.cc
+#include <iostream>
+
+auto mid(int a, int b) -> int
+{
+ return (a + b) / 2;
+}
+auto main() -> int
+{
+ int i = 0, j = 0;
+ std::cout << "Enter i, j: ";
+ std::cin >> i >> j;
+ std::cout << "A number half way between " << i << " and " << j
+ << " is " << mid(i, j) << "\n";
+}
+
diff --git a/day1/solutions/min_of_three.cc b/day1/solutions/min_of_three.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7093015d3a52afb37dbb1626663148d744230b2d
--- /dev/null
+++ b/day1/solutions/min_of_three.cc
@@ -0,0 +1,21 @@
+// examples/min_of_three.cc
+#include <iostream>
+
+auto min_of_three(int a, int b, int c) -> int
+{
+ if (a <= b) {
+ if (a <= c) return a;
+ else return c;
+ } else {
+ if (b <= c) return b;
+ else return c;
+ }
+}
+auto main() -> int
+{
+ int i = 0, j = 0, k = 0;
+ std::cout << "Enter i, j and k: ";
+ std::cin >> i >> j >> k;
+ std::cout << "The smallest of the three is " << min_of_three(i, j, k) << "\n";
+}
+
diff --git a/day1/solutions/mysqrt.cc b/day1/solutions/mysqrt.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ae024aab0c80f5bace12b78040b752f83441ccba
--- /dev/null
+++ b/day1/solutions/mysqrt.cc
@@ -0,0 +1,32 @@
+#include <iostream>
+#include <cmath>
+
+auto mysqrt(double x) -> double
+{
+ const auto eps = 1.0e-12;
+ const auto eps2 = eps * eps;
+ auto r0 = 0.5 * (1. + x);
+ auto r1 = x / r0;
+ while ((r0 - r1) * (r0 - r1) > eps2) {
+ r0 = 0.5 * (r0 + r1);
+ r1 = x / r0;
+ }
+ return r1;
+}
+
+auto main() -> int
+{
+ double x{};
+ std::cout << "Enter a positive real number: ";
+ std::cin >> x;
+ if (x > 0.) {
+ auto rm = mysqrt(x);
+ auto rs = std::sqrt(x);
+ std::cout << "Square root with own function = " << rm << "\n";
+ std::cout << "Square root with standard function = " << rs << "\n";
+ std::cout << "Difference = " << rm - rs << "\n";
+ } else {
+ std::cout << "The input number needs to be positive.\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
+)";
+}