diff --git a/BarlasChpt3Ex12/CMakeLists.txt b/BarlasChpt3Ex12/CMakeLists.txt
new file mode 100644
index 0000000..3a7a3d4
--- /dev/null
+++ b/BarlasChpt3Ex12/CMakeLists.txt
@@ -0,0 +1,24 @@
+cmake_minimum_required(VERSION 3.14)
+
+project(BarlasChpt3Ex12 LANGUAGES CXX)
+
+set(CMAKE_AUTOUIC ON)
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
+find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Core)
+
+add_executable(BarlasChpt3Ex12
+  main.cpp
+)
+target_link_libraries(BarlasChpt3Ex12 Qt${QT_VERSION_MAJOR}::Core)
+
+include(GNUInstallDirs)
+install(TARGETS BarlasChpt3Ex12
+    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+)
diff --git a/BarlasChpt3Ex12/main.cpp b/BarlasChpt3Ex12/main.cpp
new file mode 100644
index 0000000..099cd9f
--- /dev/null
+++ b/BarlasChpt3Ex12/main.cpp
@@ -0,0 +1,86 @@
+#include <iostream>
+#include <QSemaphore>
+#include <QThread>
+
+/*
+ * Barlas Chpt 3 Ex 12:
+    Create three threads, each printing out the letters A, B, and C.
+    The printing must adhere to these rules:
+        • The total number of Bs and Cs that have been output at any
+          point in the output string cannot exceed the total number
+          of As that have been output at that point.
+        • After a C has been output, another C cannot be output until
+          one or more Bs have been output.
+    Use semaphores to solve the problem.
+*/
+
+class printer{
+private:
+    QSemaphore* lockBC;
+    QSemaphore* lockC;
+
+public:
+    printer(QSemaphore* lockBC, QSemaphore* lockC){
+        this->lockBC = lockBC;
+        this->lockC = lockC;
+    }
+
+    void printA(){
+        this->lockBC->release(1);
+        std::cout << "A\n";
+    }
+
+    void printB(){
+        if(this->lockBC->tryAcquire(1)){
+            if(this->lockC->available() == 0){
+                this->lockC->release(1);
+            }
+            std::cout << "B\n";
+        }
+    }
+
+    void printC(){
+        if(this->lockBC->tryAcquire(1)){
+            if(this->lockC->tryAcquire(1)){
+                std::cout << "C\n";
+            }else{
+                this->lockBC->release(1);
+            }
+        }
+    }
+};
+
+class worker : public QThread{
+private:
+    QSemaphore* lockBC;
+    QSemaphore* lockC;
+
+public:
+    worker(QSemaphore* lockBC, QSemaphore* lockC){
+        this->lockBC = lockBC;
+        this->lockC = lockC;
+    }
+
+    void run(){
+        printer print = printer(this->lockBC, this->lockC);
+        print.printA();
+        print.printB();
+        print.printC();
+    }
+};
+
+
+int main(int argc, char *argv[])
+{
+    QSemaphore lockC(1);
+    QSemaphore lockBC(0);
+
+    int N = 3;
+    worker *workers[N];
+    for(int i = 0; i < N; i++){
+        workers[i] = new worker(&lockBC, &lockC);
+        workers[i]->run();
+    }
+
+    return 0;
+}