Remove unused code and migrate to CMake build system.

cpp/intro/main.cpp

@@ -0,0 +1,44 @@
+#include <iostream>
+#include "functions.h"
+
+using namespace std;
+
+void functionB() {
+}
+
+void functionC(); // forward declaration
+void functionD(); // forward declaration
+
+int main() {
+    const char *lang = "C++";
+    std::cout << "Hello and welcome to " << lang << "!\n";
+
+    for (int i = 1; i <= 5; i++) {
+        std::cout << "i = " << i << std::endl;
+    }
+
+    // functionA(); // compiler error - function is defined after call
+    functionB(); // no error - function is defined before call
+    // functionC(); // linker error - function is declared but not defined
+    functionD(); // no error - function is declared and defined
+    functionE();
+    // functionF(); // linker error - function is defined twice
+
+    // byte b;
+    short s;
+    int i;
+    long l;
+    long long ll;
+
+    cout << "size of short: " << sizeof(s) << endl;
+    cout << "size of int: " << sizeof(i) << endl;
+    cout << "size of long: " << sizeof(l) << endl;
+    cout << "size of long long: " << sizeof(ll) << endl;
+
+    return 0;
+}
+
+void functionA() {
+}
+
+void functionD() {}