Pushing everything again, accidentally deleted my remote repository

ex1/ex1C_summation_of_specified_numbers/main.cpp

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+#include "special_sum.h"
+#include "../utils/timing.h"
+#include <iostream>
+#include <chrono>
+#include <stack>
+using namespace std;
+
+int main(int argc, char **argv)
+{
+    // check results and compare speeds
+    for(size_t n : {15, 1001, 1432987})
+    {
+        cout << "n = " << n << endl;
+        size_t sum_1, sum_2;
+
+        tic();
+        for(size_t i = 0; i < 1000; ++i)
+            sum_1 = special_sum_loop(n);
+        double time_1 = toc();
+
+        tic();
+        for(size_t i = 0; i < 1000; ++i)
+            sum_2 = special_sum_noloop(n);
+        double time_2 = toc();
+            
+        cout << "loop: " << sum_1 << "\t\tDuration: " << time_1 << endl;
+        cout << "no loop: " << sum_2 << "\t\tDuration: " << time_2 << endl << "---------------------------------------------------" << endl;
+    }
+
+    return 0;
+}

ex1/ex1C_summation_of_specified_numbers/special_sum.cpp

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+#include "special_sum.h"
+
+size_t gauss_sum(size_t n)
+{
+    return (n*(n+1))/2;
+}
+
+size_t special_sum_loop(size_t n)
+{
+    size_t sum = 0;
+    for (size_t i = 1; i < n+1; ++i)
+    {
+        if (i % 3 == 0 || i % 5 == 0)
+        {
+            sum += i;
+        }
+    }
+    return sum;
+}
+
+size_t special_sum_noloop(size_t n)
+{
+    size_t factor_3 = gauss_sum(n/3);   // dividing int by int automatically gets rounded off
+    size_t factor_5 = gauss_sum(n/5);
+    size_t factor_15 = gauss_sum(n/15);
+
+    return factor_3*3 + factor_5*5 - factor_15*15;
+}

ex1/ex1C_summation_of_specified_numbers/special_sum.h

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+#include <cstddef>
+
+/**
+  This function returns the sum of all positive integers less or equal n which are a multiples of 3 or of 5, WITH using a loop.
+  @param[in]    n         
+  @param[out]   M        
+*/
+size_t special_sum_loop(size_t n);
+
+
+/**
+  This function returns the sum of all positive integers less or equal n which are a multiples of 3 or of 5, WITHOUT using a loop.
+  Example: For n=15, we have 60 = 3+5+6+9+10+12+15 = (1+2+3+4+5)*3 + (1+2+3)*5 - 1*15
+  Formula: M = (\sum_{i=1}^{k_3} i)*3 + (\sum_{i=1}^{k_5} i)*5 - (\sum_{i=1}^{k_15} i)*15
+  @param[in]    n         
+  @param[out]   M        
+*/
+size_t special_sum_noloop(size_t n);