From c70572f1b9e4ec81a0b72ec85205df0aadfff244 Mon Sep 17 00:00:00 2001
From: "jakob.schratter" <jakob.schratter@noreply.imsc.uni-graz.at>
Date: Wed, 22 Oct 2025 15:22:07 +0200
Subject: [PATCH] Upload files to "ex1C_summation_of_specified_numbers"

---
 ex1C_summation_of_specified_numbers/main.cpp  | 31 +++++++++++++++++++
 .../special_sum.cpp                           | 28 +++++++++++++++++
 .../special_sum.h                             |  5 +++
 3 files changed, 64 insertions(+)
 create mode 100644 ex1C_summation_of_specified_numbers/main.cpp
 create mode 100644 ex1C_summation_of_specified_numbers/special_sum.cpp
 create mode 100644 ex1C_summation_of_specified_numbers/special_sum.h

diff --git a/ex1C_summation_of_specified_numbers/main.cpp b/ex1C_summation_of_specified_numbers/main.cpp
new file mode 100644
index 0000000..f469cd2
--- /dev/null
+++ b/ex1C_summation_of_specified_numbers/main.cpp
@@ -0,0 +1,31 @@
+#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;
+}
diff --git a/ex1C_summation_of_specified_numbers/special_sum.cpp b/ex1C_summation_of_specified_numbers/special_sum.cpp
new file mode 100644
index 0000000..d2860ff
--- /dev/null
+++ b/ex1C_summation_of_specified_numbers/special_sum.cpp
@@ -0,0 +1,28 @@
+#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;
+}
\ No newline at end of file
diff --git a/ex1C_summation_of_specified_numbers/special_sum.h b/ex1C_summation_of_specified_numbers/special_sum.h
new file mode 100644
index 0000000..49d579a
--- /dev/null
+++ b/ex1C_summation_of_specified_numbers/special_sum.h
@@ -0,0 +1,5 @@
+#include <cstddef>
+
+size_t special_sum_loop(size_t n);
+
+size_t special_sum_noloop(size_t n);
\ No newline at end of file