diff --git a/README.md b/README.md
index d224c31..081651b 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,8 @@
 # project-euler
 
-Several project euler problems solved in C++
\ No newline at end of file
+Several project euler problems solved in C++
+
+#Euler problem 1 :
+
+<p>If we list all the natural numbers below $10$ that are multiples of $3$ or $5$, we get $3, 5, 6$ and $9$. The sum of these multiples is $23$.</p>
+<p>Find the sum of all the multiples of $3$ or $5$ below $1000$.</p>
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diff --git a/euler/euler/euler.cpp b/euler/euler/euler.cpp
index 637c42d..62db2f0 100644
--- a/euler/euler/euler.cpp
+++ b/euler/euler/euler.cpp
@@ -2,19 +2,27 @@
 //
 
 #include <iostream>
+#include <cassert> 
+#include "euler_p1.h"
+
+
+
+void unit_tests() {
+
+    assert(euler1(10) == 23);
+
+    std::cout << "All tests passed! continues main." << std::endl;
+}
+
+int euler_p1() {
+    int res = euler1(1000);
+    return res;
+}
 
 int main()
 {
-    std::cout << "Hello World!\n";
+    unit_tests();
+    
+    std::cout << "the result for problem 1 = " << euler_p1() << std::endl;
 }
 
-// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
-// Debug program: F5 or Debug > Start Debugging menu
-
-// Tips for Getting Started: 
-//   1. Use the Solution Explorer window to add/manage files
-//   2. Use the Team Explorer window to connect to source control
-//   3. Use the Output window to see build output and other messages
-//   4. Use the Error List window to view errors
-//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
-//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file
diff --git a/euler/euler/euler.vcxproj b/euler/euler/euler.vcxproj
index 6ff586c..6ab2224 100644
--- a/euler/euler/euler.vcxproj
+++ b/euler/euler/euler.vcxproj
@@ -128,6 +128,10 @@
   </ItemDefinitionGroup>
   <ItemGroup>
     <ClCompile Include="euler.cpp" />
+    <ClCompile Include="euler_p1.cpp" />
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="euler_p1.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
diff --git a/euler/euler/euler.vcxproj.filters b/euler/euler/euler.vcxproj.filters
index 4d134af..104f92e 100644
--- a/euler/euler/euler.vcxproj.filters
+++ b/euler/euler/euler.vcxproj.filters
@@ -18,5 +18,13 @@
     <ClCompile Include="euler.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="euler_p1.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="euler_p1.h">
+      <Filter>Source Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>
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diff --git a/euler/euler/euler_p1.cpp b/euler/euler/euler_p1.cpp
new file mode 100644
index 0000000..b5c3660
--- /dev/null
+++ b/euler/euler/euler_p1.cpp
@@ -0,0 +1,19 @@
+#include "euler_p1.h"
+
+/*
+If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
+Find the sum of all the multiples of 3 or 5 below 1000.
+
+*/
+
+int euler1(int limit) {
+    int result = 0;
+	for (size_t i = 1; i < limit; i++)
+	{
+		if (i % 3 == 0 || i % 5 == 0)
+		{
+			result += i;
+		}
+	}
+    return result;
+}
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diff --git a/euler/euler/euler_p1.h b/euler/euler/euler_p1.h
new file mode 100644
index 0000000..a4be6de
--- /dev/null
+++ b/euler/euler/euler_p1.h
@@ -0,0 +1,12 @@
+#pragma once
+/**
+ * @brief Solves Euler problem 1: Multiples of 3 and 5
+ *
+ * This function calculates the sum of all the multiples of 3 or 5 below a given number.
+ *
+ * @param limit The upper limit for the range to consider (should be positive).
+ * @return The sum of multiples of 3 or 5 below the given limit.
+ *
+ * @note This function only works with positive integer inputs.
+ */
+int euler1(int limit);
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