Added: C++ projects

CPlusPlus/Forward_Declaration/.idea/Forward_Declaration.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module classpath="CIDR" type="CPP_MODULE" version="4" />

CPlusPlus/Forward_Declaration/CMakeLists.txt

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+cmake_minimum_required(VERSION 4.3)
+project(Forward_Declaration)
+
+set(CMAKE_CXX_STANDARD 20)
+
+add_executable(Forward_Declaration main.cpp
+        functions.h
+        functions.cpp)

CPlusPlus/Forward_Declaration/functions.cpp

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+//
+// Created by David Hackbarth on 21.09.26.
+//
+#include "functions.h"
+
+void functionE() {} // defined

CPlusPlus/Forward_Declaration/functions.h

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+//
+// Created by David Hackbarth on 21.09.26.
+//
+
+#pragma once
+
+#ifndef FORWARD_DECLARATION_FUNCTIONS_H
+#define FORWARD_DECLARATION_FUNCTIONS_H
+
+void functionE(); // declared
+
+// void functionF() {} // declared & defined, linker error when included multiple times
+
+#endif //FORWARD_DECLARATION_FUNCTIONS_H

CPlusPlus/Forward_Declaration/main.cpp

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+#include "functions.h"
+
+void functionB() {} // declared & defined
+void functionC(); // declared
+void functionD(); // declared
+
+int main()
+{
+    // functionA(); // compiler error, because functionA is declared & defined after it is called
+    functionB(); // no error
+    // functionC(); // linker error, because functionC is declared but not defined
+    functionD(); // no error
+    functionE(); // no error
+
+    return 0;
+}
+
+void functionA() {} // declared & defined
+
+void functionD() {} // defined
+
+// void functionE() {} // linker error, because functionE is defined multiple times