From 848dba33144f55c29a02b970228ba58e699b13b5 Mon Sep 17 00:00:00 2001
From: Nathan Mannall <n.mannall@epcc.ed.ac.uk>
Date: Fri, 16 Jan 2026 14:27:29 +0000
Subject: [PATCH] Add solution to new templates exercise

---
 solutions/.gitignore                  |  1 +
 solutions/5-templates/part2/Makefile  | 10 +++++
 solutions/5-templates/part2/array.hpp | 54 ++++++++++++++++++++++++++
 solutions/5-templates/part2/main.cpp  | 56 +++++++++++++++++++++++++++
 4 files changed, 121 insertions(+)
 create mode 100644 solutions/5-templates/part2/Makefile
 create mode 100644 solutions/5-templates/part2/array.hpp
 create mode 100644 solutions/5-templates/part2/main.cpp

diff --git a/solutions/.gitignore b/solutions/.gitignore
index 1754788..ed352dd 100644
--- a/solutions/.gitignore
+++ b/solutions/.gitignore
@@ -1,5 +1,6 @@
 # Ignore executables created by the solutions
 4-pointers/pointers
+5-templates/part2/main
 6.1-my-array/part1
 6.1-my-array/part2
 6.1-my-array/part3
diff --git a/solutions/5-templates/part2/Makefile b/solutions/5-templates/part2/Makefile
new file mode 100644
index 0000000..7931774
--- /dev/null
+++ b/solutions/5-templates/part2/Makefile
@@ -0,0 +1,10 @@
+CXXFLAGS = --std=c++20
+
+main : main.o
+	$(CXX) $^ -o $@
+
+run : main
+	./main
+
+clean :
+	rm -rf *.o main
diff --git a/solutions/5-templates/part2/array.hpp b/solutions/5-templates/part2/array.hpp
new file mode 100644
index 0000000..cb4ee41
--- /dev/null
+++ b/solutions/5-templates/part2/array.hpp
@@ -0,0 +1,54 @@
+#ifndef CPPEX_ARRAY_HPP
+#define CPPEX_ARRAY_HPP
+
+#include <iostream>
+
+// Add template parameters to set the data type and array size at compile time
+template <typename T, unsigned int N>
+class FixedSizeArray {
+
+private:
+    T data[N];
+
+public:
+
+    FixedSizeArray() {
+        for (int i = 0; i < N; ++i) {
+            data[i] = T();  // Initialise values by calling type's default constructor
+        }
+    }
+
+    // Overload the [] operator to provide access to the array elements
+    T& operator[](int index) {
+        return data[index];
+    }
+
+    const T& operator[](int index) const {
+        return data[index];
+    }
+
+    // Create function size() that returns the size of the array
+    unsigned int size() const { return N; }
+
+    // Create function reduce() that sums all elements of the array
+    T reduce() const {
+        T result = data[0];
+        for (int i = 1; i < N; ++i) {
+            result += data[i];
+        }
+        return result;
+    }
+
+    // Create function doubleInPlace() that doubles each element of the array
+    void doubleInPlace() {
+        if constexpr (std::is_arithmetic<T>()) {
+            for (int i = 0; i < N; ++i) {
+                data[i] *= 2;
+            }
+        } else {
+            std::cout << "ERROR: Cannot double array values. Data type is not arithmetic" << std::endl;
+        }
+    }
+};
+
+#endif
diff --git a/solutions/5-templates/part2/main.cpp b/solutions/5-templates/part2/main.cpp
new file mode 100644
index 0000000..0d9c1fe
--- /dev/null
+++ b/solutions/5-templates/part2/main.cpp
@@ -0,0 +1,56 @@
+#include "array.hpp"
+
+void print(auto&& arr) {
+    /* Helper function to print the contents of a FixedSizeArray */
+    std::cout << "[ " << arr[0];
+    for (int i = 1; i < arr.size(); ++i) {
+        std::cout << ", " << arr[i];
+    }
+    std::cout << " ]" << std::endl;
+}
+
+int main() {
+    // Initialise an empty fixed size array of 5 integers
+    FixedSizeArray<int, 5> arr;
+    std::cout << "Array size: " << arr.size() << std::endl;
+    print(arr);
+
+    // Use a for loop to set the array values. E.g. 1-5
+    for (int i = 0; i < arr.size(); ++i) {
+        arr[i] = i + 1;
+    }
+    print(arr);
+
+    // Call doubleInPlace() and print the new array
+    arr.doubleInPlace();
+    print(arr);
+
+    // Initialise an empty fixed size array of 5 integers with the const specifier
+    const FixedSizeArray<int, 5> constArr = arr;
+    print(constArr);
+
+    // Print the output of calling reduce()
+    std::cout << constArr.reduce() << std::endl;
+
+    // Check you get a compile time error if you try to set an element value in the
+    // const array, or if you call doubleInPlace()
+    // constArr[0] = 1;
+    // constArr.doubleInPlace();
+
+    // Initialise a fixed size array of strings with element values "Hello" and "World!"
+    FixedSizeArray<std::string, 2> strArr;
+    strArr[0] = "Hello";
+    strArr[1] = "World!";
+    std::cout << "strArr size: " << strArr.size() << std::endl;
+    print(strArr);
+
+    // Print the output of calling reduce() on strArr
+    std::cout << "strArr reduction: " << strArr.reduce() << std::endl;
+
+    // Call doubleInPlace(). What happens? Can you explain this?
+    // EXTENSION: Can you change the behaviour of doubleInPlace for non numeric data types?
+    // E.g. Just print an error and leave the array unchanged.
+    // Hint: You may want to search for useful type traits, and look up 'if constexpr'.
+    strArr.doubleInPlace();
+    print(strArr);
+}