Updated to initial implementation using cpp.

Exercises.cpp

@@ -0,0 +1,65 @@
+#include <iostream>
+#include <vector>
+#include "Exercises.h"
+
+// Gives multiple of all multiples of 3 or 5 under given number.
+int Ex1(int in) {
+    int out = 0;
+
+    for (int i = 3; i < in; i += 3) out += i;
+    for (int i = 5, t = 1; i < in; i += 5, t++) {
+        if (t == 3) t = 0; 
+        else out += i; 
+    }
+    return out;
+}
+
+// Gives multiple of all even fibonacci sequence values under given number
+int Ex2(int in) {
+    int v1 = 0, v2 = 1, f = 0, out = 0;
+    while (true) {
+        // calc fibonacci value
+        f = v1 + v2;
+        v1 = v2;
+        v2 = f;
+
+        // stop if fibonacci value over max
+        if (in < f) break;
+        // skip if uneven
+        if ((f & 0b1) == 1) continue;
+
+        // sum
+        out += f;
+    }
+    return out;
+}
+
+/*
+Works but needs to be optimised for large number: 600851475143
+*/
+// Gives biggest prime factor of given number
+unsigned long long Ex3(unsigned long long in) {
+    vector<unsigned long long> primes = { 2 };
+    unsigned long long biggest_prime = -1;
+
+    for (unsigned long long num = 2; num <= in; num++)
+    {
+        // Find prime
+        bool isPrime = true;
+        for (auto prime : primes)
+        {
+            isPrime = num % prime != 0;
+            if (!isPrime) break;
+        }
+        if (!isPrime) continue;
+        primes.push_back(num);
+
+        // Is number factor of input, if not go to next number.
+        if (in % num != 0) continue;
+
+        // Save current prime as biggest prime and promote other factor as new max.
+        biggest_prime = num;
+        in = in / num;
+    }
+    return biggest_prime;
+}