helloworld tutorial

Author: stgm

helloworld/index.md

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+# Hello
+
+Here's your first C program:
+
+    #include <stdio.h>
+
+    int main(void)
+    {
+        printf("hello, world\n");
+    }
+
+You have seen it in lecture, and now you're ready to try running it yourself.
+
+
+## Dive into your development environment
+
+### Instructions for Mac OS
+
+Go to your Terminal. You should find that its "prompt" resembles the below.
+
+    jharvard@somewhere ~ %
+
+Here on out, to execute (i.e., run) a command means to type it into a terminal window and then hit Enter. Commands are "case-sensitive," so be sure not to type in uppercase when you mean lowercase or vice versa.
+
+Now execute
+
+    cd ~/Documents/Programming/
+
+to move yourself into (i.e., open) that directory. Your prompt should now resemble the below.
+
+    jharvard@somewhere Programming %
+
+If not, retrace your steps and see if you can determine where you went wrong.
+
+Now, open Atom, point to the File menu and choose New. This will open a new editor with a blank "Untitled1" file in it. First thing to do is to give it a name and save it into your new directory. Press **CTRL-S** or **Cmd-S** to open the file dialog. For **Filename**, type `hello.c`. Then below, choose (click) the `Documents`, then the `Programming` folder that you just created and click on **Save**.
+
+In your new file, type the C code for "Hello, World" as seen above. Save it once more.
+
+### Instructions for Windows
+
+Go to your Terminal. You should find that its "prompt" resembles the below.
+
+    jharvard@COMPUTER:~$
+
+Here on out, to execute (i.e., run) a command means to type it into a terminal window and then hit Enter. Commands are "case-sensitive," so be sure not to type in uppercase when you mean lowercase or vice versa.
+
+Now execute
+
+    cd /mnt/c/Users/<Windows User Name>/Documents/Programming/
+
+to move yourself into (i.e., open) that directory. Your prompt should now resemble the below.
+
+    jharvard@COMPUTER:Programming$
+
+If not, retrace your steps and see if you can determine where you went wrong.
+
+Now, open Atom, point to the File menu and choose New. This will open a new editor with a blank "Untitled1" file in it. First thing to do is to give it a name and save it into your new directory. Press **CTRL-S** or **Cmd-S** to open the file dialog. For **Filename**, type `hello.c`. Then below, choose (click) the `Documents`, then the `Programming` folder that you just created and click on **Save**.
+
+In your new file, type the C code for "Hello, World" as seen above. Save it once more.
+
+
+## Listing files
+
+Next, type precisely the below (in lowercase), then hit Enter:
+
+    ls
+
+You should see just `Makefile` and `hello.c`. That's because you've just listed the files in that same folder, this time using a command-line interface (CLI), using just your keyboard, rather than the graphical user interface (GUI) represented by that folder icon. In particular, you *executed* (i.e., ran) a command called `ls`, which is shorthand for "list." (It's such a frequently used command that its authors called it just `ls` to save keystrokes.) Make sense?
+
+
+## Compiling programs
+
+Now, before we can execute the program at right, recall that we must *compile* it with a *compiler* (e.g., `clang`), translating it from *source code* into *machine code* (i.e., zeroes and ones). Execute the command below to do just that:
+
+    clang hello.c
+
+And then execute this one again:
+
+    ls
+
+This time, you should see not only `hello.c` but `a.out` listed as well? (You can see the same graphically if you click that folder icon again.) That's because `clang` has translated the source code in `hello.c` into machine code in `a.out`, which happens to stand for "assembler output," but more on that another time.
+
+Now run the program by executing the below.
+
+    ./a.out
+
+Hello, world, indeed!
+
+
+## Naming programs
+
+Now, `a.out` isn't the most user-friendly name for a program. Let's compile `hello.c` again, this time saving the machine code in a file called, more aptly, `hello`. Execute the below.
+
+    clang -o hello hello.c
+
+Take care not to overlook any of those spaces therein! Then execute this one again:
+
+    ls
+
+You should now see not only `hello.c` (and `a.out` from before) but also `hello` listed as well? That's because `-o` is a *command-line argument*, sometimes known as a *flag* or a *switch*, that tells `clang` to output (hence the `o`) a file called `hello`. Execute the below to try out the newly named program.
+
+    ./hello
+
+Hello there again!
+
+
+## Making things easier
+
+Recall from lecture that we can automate the process of executing `clang`, letting `make` figure out how to do so for us, thereby saving us some keystrokes.
+
+Now execute the below to compile your program one last time.
+
+    make hello
+
+You should see that `make` executes `clang` with even more command-line arguments for you? More on those, too, another time!
+
+Now execute the program itself one last time by executing the below.
+
+    ./hello
+
+Phew!