Hello

Getting Started

Recall that Visual Studio Code (aka VS Code) is a popular “integrated development environment” (IDE) via which you can write code. So that you don’t have to download, install, and configure your own copy of VS Code, we’ll use a cloud-based version instead that has everything you’ll need pre-installed.

Log into code.cs50.io using your GitHub account. Once your “codespace” loads, you should see that, by default, VS Code is divided into three regions. Toward the top of VS Code is your “text editor”, where you’ll write all of your programs. Toward the bottom of is a “terminal window”, a command-line interface (CLI) that allows you to explore your codespace’s files and directories (aka folders), compile code, and run programs. And on the left is your file “explorer,” a graphical user interface (GUI) via which you can also explore your codespace’s files and directories.

Start by clicking inside your terminal window, then execute cd by itself. You should find that its “prompt” resembles the below.

Click inside of that terminal window and then type

mkdir hello

followed by Enter in order to make a directory called hello in your codespace. Take care not to overlook the space between mkdir and hello or any other character for that matter!

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 hello

to move yourself into (i.e., open) that directory. Your prompt should now resemble the below.

hello/ $

If not, retrace your steps and see if you can determine where you went wrong!

Shall we have you write your first program? Execute

code hello.c

to create a new file called hello.c, which should open automatically in your codespace’s text editor. As soon as you save the file with command-S (on macOS) or control-S (on Windows), it should also appear in your codespace’s explorer.

Proceed to write your first program by typing precisely these lines into hello.c:

#include <stdio.h>

int main(void)
{
    printf("hello, world\n");
}

Notice how VS Code adds “syntax highlighting” (i.e., color) as you type, though VS Code’s choice of colors might differ from this problem set’s. Those colors aren’t actually saved inside of the file itself; they’re just added by VS Code to make certain syntax stand out. Had you not saved the file as hello.c from the start, VS Code wouldn’t know (per the filename’s extension) that you’re writing C code, in which case those colors would be absent.

Listing Files

Next, in your terminal window, immediately to the right of the prompt (hello/ $), execute

ls

You should see just hello.c? That’s because you’ve just listed the files in your hello folder. In particular, you executed 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 hello.c program, recall that we must compile it with a compiler, translating it from source code into machine code (i.e., zeroes and ones). Execute the command below to do just that:

make hello

And then execute this one again:

ls

This time, you should see not only hello.c but hello listed as well? You’ve now translated the source code in hello.c into machine code in hello.

Now execute the program itself by executing the below.

./hello

Hello, world, indeed!

Getting User Input

Suffice it to say, no matter how you compile or execute this program, it only ever prints hello, world. Let’s personalize it a bit, just as we did in class.

Modify this program in such a way that it first prompts the user for their name and then prints hello, so-and-so, where so-and-so is their actual name.

As before, be sure to compile your program with:

make hello

And be sure to execute your program, testing it a few times with different inputs, with:

./hello

Walkthrough

Here’s a “walkthrough” (i.e., tour) of this problem, if you’d like a verbal overview of what to do too!

Hints

Don’t recall how to prompt the user for their name?

Recall that you can use get_string as follows, storing its return value in a variable called name of type string.

string name = get_string("What's your name? ");

Don’t recall how to format a string?

Don’t recall how to join (i.e., concatenate) the user’s name with a greeting? Recall that you can use printf not only to print but to format a string (hence, the f in printf), a la the below, wherein name is a string.

printf("hello, %s\n", name);

Use of undeclared identifier?

Seeing the below, perhaps atop other errors?

error: use of undeclared identifier 'string'; did you mean 'stdin'?

Recall that, to use get_string, you need to include cs50.h (in which get_string is declared) atop a file, as with:

#include <cs50.h>

How to Test Your Code

Execute the below to evaluate the correctness of your code using check50, a command-line program that will output happy faces whenever your code passes CS50’s automated tests and sad faces whenever it doesn’t! But be sure to compile and test it yourself as well!

check50 cs50/problems/2022/spring/hello

Execute the below to evaluate the style of your code using style50, a command-line program that will output additions (in green) and deletions (in red) that you should make to your program in order to improve its style. If you have trouble seeing those colors, style50 supports other modes too!

style50 hello.c

How to Submit

Download your hello.c file by control-clicking or right-clicking on the file in your codespace’s file browser and choosing Download.
Go to CS50’s Gradescope page.
Click “Problem Set 1: Hello”.
Drag and drop your hello.c file to the area that says “Drag & Drop”. Be sure it has that exact filename! If you upload a file with a different name, the autograder likely will fail when trying to run it, and ensuring you have uploaded files with the correct filename is your responsibility!
Click “Upload”.

You should see a message that says “Problem Set 1: Hello submitted successfully!” You may not see a score just yet, but if you see the message then we’ve received your submission!