Add first exercise: Hello world (#6)

* add key_features

* update gitignore with Cairo-specific files

* add hello-world exercise + format config.json

* update key_features to include 6 items

* Create strings concept

---------

Co-authored-by: Nenad <nenad@better.giving>

.gitignore

@@ -2,3 +2,5 @@
 .DS_Store
 bin/configlet
 bin/configlet.exe
+**/target
+exercises/*/*/Scarb.lock

concepts/strings/.meta/config.json

@@ -0,0 +1,7 @@
+{
+    "blurb": "ByteArray is a sequence of ASCII characters longer than 31 characters, written using double quotes",
+    "authors": [
+        "misicnenad"
+    ],
+    "contributors": []
+}

concepts/strings/about.md

@@ -0,0 +1 @@
+# String

concepts/strings/introduction.md

@@ -0,0 +1,3 @@
+# Introduction
+
+In Cairo, there's no native type for strings. Instead, you can use a single `felt252` to store a short string of up to 31 characters, or a `ByteArray` for strings of arbitrary length. Short strings use single quotes and `ByteArray` uses double quotes. All characters must follow the ASCII standard.

concepts/strings/links.json

@@ -0,0 +1,14 @@
+[
+    {
+        "url": "https://book.cairo-lang.org/ch02-02-data-types.html#string-types",
+        "description": "String types in the Cairo book"
+    },
+    {
+        "url": "https://starknet-by-example.voyager.online/getting-started/basics/bytearrays-strings.html",
+        "description": "Starknet by Example section on Strings and ByteArrays"
+    },
+    {
+        "url": "https://docs.starknet.io/architecture-and-concepts/smart-contracts/serialization-of-cairo-types/#serialization_of_byte_arrays",
+        "description": "Starknet docs explaining how ByteArray is implemented and how it's serialized"
+    }
+]

config.json

@@ -34,22 +34,72 @@
     ]
   },
   "exercises": {
-    "concept": [],
-    "practice": []
+    "practice": [
+      {
+        "slug": "hello-world",
+        "name": "Hello World",
+        "uuid": "1a0e23d9-e8f9-493a-af46-2be040173b64",
+        "practices": [
+          "strings"
+        ],
+        "prerequisites": [],
+        "difficulty": 1,
+        "topics": [
+          "test_driven_development"
+        ]
+      }
+    ]
   },
-  "concepts": [],
-  "key_features": [],
+  "concepts": [
+    {
+      "uuid": "4eb800f7-f6c5-4b28-8492-229b6a51829e",
+      "slug": "strings",
+      "name": "Strings"
+    }
+  ],
+  "key_features": [
+    {
+      "title": "Developer-friendly",
+      "content": "Write Rust-like code and generate proofs for program execution - math isn't a barrier.",
+      "icon": "easy"
+    },  
+    {
+      "title": "Provable",
+      "content": "Produces provable programs, making it possible to compute trustworthy values on untrusted machines.",
+      "icon": "safe"
+    },
+    {
+      "title": "Efficient",
+      "content": "Cairo compiles down to an ad-hoc assembly engineered specifically for efficient proof generation.",
+      "icon": "fast"
+    },
+    {
+      "title": "Immutable",
+      "content": "Cairo uses the immutable memory model, improving data integrity and security.",
+      "icon": "immutable"
+    },
+    {
+      "title": "General purpose",
+      "content": "From onchain gaming to provable ML, Cairo makes building trustless applications possible.",
+      "icon": "general-purpose"
+    },
+    {
+      "title": "Innovative",
+      "content": "Cairo is a fast-growing language that keeps delivering new and exciting features to its developers.",
+      "icon": "evolving"
+    }
+  ],
   "tags": [
+    "execution_mode/compiled",
     "paradigm/functional",
     "paradigm/imperative",
     "paradigm/procedural",
-    "typing/static",
-    "typing/strong",
-    "execution_mode/compiled",
-    "platform/windows",
-    "platform/mac",
     "platform/linux",
+    "platform/mac",
+    "platform/windows",
     "runtime/standalone_executable",
+    "typing/static",
+    "typing/strong",
     "used_for/artificial_intelligence",
     "used_for/backends",
     "used_for/financial_systems",

exercises/practice/hello-world/.docs/instructions.md

@@ -0,0 +1,16 @@
+# Instructions
+
+The classical introductory exercise.
+Just say "Hello, World!".
+
+["Hello, World!"][hello-world] is the traditional first program for beginning programming in a new language or environment.
+
+The objectives are simple:
+
+- Modify the provided code so that it produces the string "Hello, World!".
+- Run the test suite and make sure that it succeeds.
+- Submit your solution and check it at the website.
+
+If everything goes well, you will be ready to fetch your first real exercise.
+
+[hello-world]: https://en.wikipedia.org/wiki/%22Hello,_world!%22_program

exercises/practice/hello-world/.meta/config.json

@@ -0,0 +1,20 @@
+{
+  "authors": [
+    "misicnenad"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.cairo",
+      "Scarb.toml"
+    ],
+    "test": [
+      "src/tests.cairo"
+    ],
+    "example": [
+      ".meta/example.cairo"
+    ]
+  },
+  "blurb": "Exercism's classic introductory exercise. Just say \"Hello, World!\".",
+  "source": "This is an exercise to introduce users to using Exercism",
+  "source_url": "https://en.wikipedia.org/wiki/%22Hello,_world!%22_program"
+}

exercises/practice/hello-world/.meta/example.cairo

@@ -0,0 +1,3 @@
+fn hello() -> ByteArray {
+    "Hello, World!"
+}

exercises/practice/hello-world/.meta/tests.toml

@@ -0,0 +1,13 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[af9ffe10-dc13-42d8-a742-e7bdafac449d]
+description = "Say Hi!"

exercises/practice/hello-world/Scarb.toml

@@ -0,0 +1,4 @@
+[package]
+name = "hello_world"
+version = "0.1.0"
+edition = "2023_11"

exercises/practice/hello-world/src/lib.cairo

@@ -0,0 +1,7 @@
+// ByteArray is a string that's not limited to 31 characters, you'll learn more about this later
+fn hello() -> ByteArray {
+    "Goodbye, Mars!"
+}
+
+#[cfg(test)]
+mod tests;

exercises/practice/hello-world/src/tests.cairo

@@ -0,0 +1,4 @@
+#[test]
+fn test_hello_world() {
+    assert_eq!(hello_world::hello(), "Hello, World!");
+}