(backend) lang: hello world

backend/cPlusPlus/README_c_plus_plus.md

@@ -0,0 +1,3 @@
+
+
+[pointer](pointer.md)

backend/cPlusPlus/pointer.md

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+
+
+## Dangling pointer
+
+A dangling pointer is a (non-NULL) pointer which points to unallocated (already freed) memory area.
+
+[wiki](https://en.wikipedia.org/wiki/Dangling_pointer)

backend/java/README_java.md

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+
+[install](backend/java/install.md)

backend/java/hello_world.md

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+
+
+## Code
+
+```java
+class Test  
+{  
+    public static void main(String []args)  
+    {  
+        System.out.println("My First Java Program.");  
+    }  
+};
+```
+
+
+## Compile
+
+To compile the program, we must run the Java compiler (javac), with the name of the source file on the “command prompt” like as follows
+
+If everything is OK, the `javac` compiler creates a file called “Test.class” containing the byte code of the program.
+
+```sh
+javac HelloWorld.java
+```
+
+## Execute
+
+- Create the program by typing it into a text editor and saving it to a file – HelloWorld.java.
+- Compile it by typing “javac HelloWorld.java” in the terminal window.
+- Execute (or run) it by typing “java HelloWorld” in the terminal window.
+
+```sh
+java HelloWorld
+```
+
+## Resource
+
+[GfG | hello world ex](https://www.geeksforgeeks.org/java-hello-world-program/)

backend/ruby/README_ruby.md

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 [documentation](backend/ruby/documentation.md)
 
-[[hello_world]]
+[[backend/ruby/hello_world]]
 
 [[backend/ruby/ternary]]