✨ (concept) Add new concept exercise cars-assemble

This is inspired by the same in csharp track. Provides a gentle introduction to variable assignment, if-statements and numbers.

config.json

@@ -35,6 +35,21 @@
   },
   "exercises": {
     "concept": [
+      {
+        "slug": "cars-assemble",
+        "uuid": "1d0e6e2c-c319-48bc-8626-7b3c98473f42",
+        "name": "Cars Assemble",
+        "difficulty": 1,
+        "concepts": [
+          "if-statements",
+          "assignment",
+          "numbers"
+        ],
+        "prerequisites": [
+          "booleans"
+        ],
+        "status": "wip"
+      },
       {
         "slug": "lucians-luscious-lasagna",
         "uuid": "29a2d3bd-eec8-454d-9dba-4b2d7d071925",

exercises/concept/cars-assemble/.docs/hints.md

@@ -0,0 +1,34 @@
+# Hints
+
+## General
+
+- [Rust book][rust-book-data-types] on Integers and Floating point numbers.
+
+## 1. Calculate the success rate
+
+- Determining the success rate can be done through a [conditional statement][if-statement].
+
+## 2. Calculate the production rate per second
+
+- Use `.into()` to convert `i32` to `f64`.
+- Use the `success_rate()` method you wrote earlier to determine the success rate.
+- Rust does not allow for multiplication to be applied to two different number
+  types (such as an `i32` and a `f64`). Both must be of the same type.
+- Numbers can be compared using the built-in comparision and equality operators.
+  Checkout [full list of operators][operators-list] supported by Rust.
+## 3. Calculate the number of working items produced per second
+
+- Use `.into()` to convert `i32` to `f64`.
+- Rounding a float to a certain precision (here 1 decimal places) can be done using:
+   ```rust
+   let my_float = 3.166;
+   let rounded = (my_float * 10.0).round() / 10.0;
+   // => 3.2
+   ```
+   Read more on this [StackOverflow answer][stackoverflow-rounding].
+
+[if-statement]: https://doc.rust-lang.org/rust-by-example/flow_control/if_else.html#ifelse
+[stackoverflow-rounding]: https://stackoverflow.com/a/28656825
+[operators-list]:https://doc.rust-lang.org/book/appendix-02-operators.html#operators
+[rust-book-data-types]:
+    https://doc.rust-lang.org/book/ch03-02-data-types.html#integer-types

exercises/concept/cars-assemble/.docs/instructions.md

@@ -0,0 +1,51 @@
+# Instructions
+
+In this exercise you'll be writing code to analyze the production of an assembly line in a car factory.
+The assembly line's speed can range from `0` (off) to `10` (maximum).
+
+At its lowest speed (`1`), `221` cars are produced each hour. The production increases linearly with the speed.
+So with the speed set to `4`, it should produce `4 * 221 = 884` cars per hour. 
+However, higher speeds increase the likelihood that faulty cars are produced, which then have to be discarded.
+
+You have three tasks.
+
+## 1. Calculate the success rate
+
+Implement the `success_rate()` function to calculate the ratio of an item being
+created without error for a given speed.
+The following table shows how speed influences the success rate:
+
+- `0`: 0% success rate.
+- `1` to `4`: 100% success rate.
+- `5` to `8`: 90% success rate.
+- `9`: 80% success rate.
+- `10`: 77% success rate.
+
+```rust
+success_rate(10)
+// => 0.77
+```
+
+Note that the value returned is a `f64`.
+
+## 2. Calculate the production rate per hour
+
+Implement the `production_rate_per_hour()` function to calculate the assembly line's production rate per hour, taking into account its success rate:
+
+```rust
+production_rate_per_hour(6)
+// => 1193.4
+```
+
+Note that the value returned is a `f64`.
+
+## 3. Calculate the number of working items produced per minute
+
+Implement the `working_items_per_minute()` function to calculate how many working cars are produced per minute:
+
+```rust
+working_items_per_minute(6)
+// => 19
+```
+
+Note that the value returned is an `i32`.

exercises/concept/cars-assemble/.docs/introduction.md

@@ -0,0 +1,180 @@
+# Introduction
+
+## Numbers
+
+There are two different types of numbers in Rust:
+
+- Integers: numbers with no digits behind the decimal separator (whole numbers). Examples are `-6`, `0`, `1`, `25`, `976` and `500000`.
+- Floating-point numbers: numbers with zero or more digits behind the decimal separator. Examples are `-2.4`, `0.1`, `3.14`, `16.984025` and `1024.0`.
+
+The two default numeric types in Rust are `i32` and `f64`. An `i32` is a 32-bit integer and a `f64` is a 64-bit floating-point number.
+
+Arithmetic is done using the standard arithmetic operators. Numbers can be
+compared using the standard numeric comparison operators and the equality (`==`)
+and inequality (`!=`) operators.
+
+## Assignment
+
+The following syntax can be used to define a variable and assign a value to it.
+
+```rust
+let my_variable = 5;
+```
+
+The above defines a variable with value 5 which automatically makes its type as
+`i32`. The value of this variable cannot be changed.
+In Rust, `snake_case` is used to define the name of a variable.
+
+To create a variable that can be assigned a different value one can use `mut`
+keyword:
+
+```rust
+let mut my_variable = 5;
+my_variable = 10;
+```
+
+In Rust, integers and floats are different types hence you cannot assign a
+float to an integer variable and vice-versa. Not even if the values seem equal:
+
+```rust
+let my_int = 5;
+let my_float = my_int; // => panic
+
+let my_float2 = 5.0;
+let my_int2 = my_float2; // => panic
+```
+
+### Constants
+Like immutable variables, *constants* are values that are bound to a name and
+are not allowed to change, but there are a few differences between constants
+and variables.
+
+- First, you aren’t allowed to use `mut` with constants.
+- Constants aren’t just immutable by default—they’re always immutable.
+- You declare constants using the `const` keyword instead of the `let` keyword, and the type of the value *must* be annotated.
+- Constants can be declared in any scope, including the global scope, which makes them useful for values that many parts of code need to know about.
+- The last difference is that constants may be set only to a constant expression, not the result of a value that could only be computed at runtime.
+
+Here’s an example of a constant declaration:
+
+```rust
+const SECONDS_IN_A_MINUTE: u32 = 60;
+```
+
+In Rust, constants are defined using `CAPITAL_SNAKE_CASE`.
+
+### Rust requires explicit conversion between types
+
+Using the `.into()` method:
+
+```rust
+let my_int = 50;
+let my_float: f64 = my_int.into(); // works as expected
+```
+
+Note that this requires specifying the variable type explicitly.
+
+As an `i32` has less precision than a `f64`, converting from an `i32` to a `f64` is safe and lossless. However, converting from a `f64` to an `i32` could mean losing data.
+
+## Numeric Operators
+
+Rust supports various operators on integers and floats.
+
+Take a look at the following table that illustrates how each operator behaves with integers and floats.
+
+| Symbol | Integer                 | Floating Point |
+|--------|-------------------------|----------------|
+| `+`    | Addition                | Addition       |
+| `-`    | Subtraction             | Subtraction    |
+| `*`    | Multiplication          | Multiplication |
+| `/`    | Division*               | Division       |
+| `%`    | Remainder**             | Remainder      |
+
+\* Integer division rounds towards zero.
+
+\*\* Rust uses a remainder defined with [truncating division].
+Given `remainder = dividend % divisor`, the remainder will have the same sign as the dividend.
+
+Note that both operands of an operator must be of same type.
+e.g. For `+` operator, an integer cannot be added to a float and vice-versa.
+
+Following example demonstrates usage for these operators.
+
+```rust
+let result_1 = 3 + 6;
+// => 9
+let result_2 = 5.5 - 1.25;
+// => 4.25
+let result_3 = -5 * 14;
+// => -70
+let result_4 = 14 / 3;
+// => 4
+let result_5 = 100 % 7;
+// => 2
+```
+
+## If Statements
+
+In this exercise you must conditionally execute logic. The most common way to do this in Rust is by using an `if/else` statement:
+
+`if` expressions start with the keyword `if`, followed by a condition. In this
+case, the condition checks whether or not the variable `number` has a value less
+than `5`.
+
+
+```rust
+let number = 3;
+
+if number < 5 {
+    println!("condition was true");
+} else {
+    println!("condition was false");
+}
+```
+
+Optionally, we can also include an `else` expression, which we chose to do here,
+to give the program an alternative block of code to execute should the condition
+evaluate to `false`.
+
+If you don’t provide an `else` expression and the condition is `false`, the program will just skip the `if` block and move on to the next bit of code.
+
+The condition of an `if` statement must be of type `bool`. Rust has no concept of
+_truthy_ values.
+
+```rust
+let number = 3;
+
+if number {
+    println!("number was three");
+}
+```
+
+The `if` condition evaluates to a value of `3` this time, and Rust throws an
+error:
+
+```txt
+  |
+4 |     if number {
+  |        ^^^^^^ expected `bool`, found integer
+
+For more information about this error, try `rustc --explain E0308`.
+error: could not compile `branches` due to previous error
+```
+
+You can use multiple conditions by combining `if` and `else` in an `else if` expression. For example:
+
+```rust
+let x = 6;
+
+if x == 5 {
+    // Execute logic if x equals 5
+} else if x > 7 {
+    // Execute logic if x greater than 7
+} else {
+    // Execute logic in all other cases
+}
+```
+
+
+[truncating division]:
+    https://en.wikipedia.org/wiki/Modulo_operation#Variants_of_the_definition

exercises/concept/cars-assemble/.gitignore

@@ -0,0 +1,8 @@
+# Generated by Cargo
+# will have compiled files and executables
+/target/
+**/*.rs.bk
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock

exercises/concept/cars-assemble/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "blurb": "Learn about numbers by analyzing the production of an assembly line.",
+  "authors": [
+    "devkabiir"
+  ],
+  "contributors": [],
+  "files": {
+    "solution": [
+      "src/lib.rs",
+      "Cargo.toml"
+    ],
+    "test": [
+      "tests/cars-assemble.rs"
+    ],
+    "exemplar": [
+      ".meta/exemplar.rs"
+    ]
+  }
+}

exercises/concept/cars-assemble/.meta/design.md

@@ -0,0 +1,26 @@
+# Design
+
+## Learning objectives
+
+- Know of the existence of the two default number types, `i32` and `f64`.
+- Understand that an `i32` represents whole numbers, and a `f64` represents floating-point numbers.
+- Know of basic operators such as multiplication, comparison and equality.
+- Know how to convert from one numeric type to another.
+- Know how to conditionally execute code using an `if` statement.
+
+## Out of scope
+
+- Any other numeric types besides `i32` and `f64` (so no `float`, `byte`, etc.).
+- Parsing a `string` to an `i32` or `f64`.
+- Converting an `i32` or `f64` to a `string`.
+
+## Concepts
+
+- `integers`: know about `i32` and `f64` types
+- `if-statements`: know how to conditionally execute code using an `if` statement.
+- `math-operators`: know the math operators; know about precedence; know the role of parentheses
+- `assignment`: know the syntax and behavior of assignment in OO languages
+
+## Prerequisites
+
+- `booleans`

exercises/concept/cars-assemble/.meta/exemplar.rs

@@ -0,0 +1,33 @@
+const PRODUCTION_RATE_PER_HOUR_FOR_DEFAULT_SPEED: i32 = 221;
+
+pub fn production_rate_per_hour(speed: i32) -> f64 {
+    let result = production_rate_per_hour_for_speed(speed) * success_rate(speed);
+
+    round_to_1_decimal(result)
+}
+
+fn round_to_1_decimal(input: f64) -> f64 {
+    (input * 10.0).round() / 10.0
+}
+
+fn production_rate_per_hour_for_speed(speed: i32) -> f64 {
+    (PRODUCTION_RATE_PER_HOUR_FOR_DEFAULT_SPEED * speed).into()
+}
+
+pub fn working_items_per_minute(speed: i32) -> i32 {
+    (production_rate_per_hour(speed) / 60.0).into()
+}
+
+pub fn success_rate(speed: i32) -> f64 {
+    if speed == 10 {
+        0.77
+    } else if speed == 9 {
+        0.8
+    } else if speed >= 5 {
+        0.9
+    } else if speed <= 0 {
+        0.0
+    } else {
+        1.0
+    }
+}

exercises/concept/cars-assemble/Cargo.toml

@@ -0,0 +1,4 @@
+[package]
+edition = "2021"
+name = "cars_assemble"
+version = "1.0.0"

exercises/concept/cars-assemble/src/lib.rs

@@ -0,0 +1,11 @@
+pub fn production_rate_per_hour(_speed: i32) -> f32 {
+    unimplemented!("Implement production_rate_per_hour")
+}
+
+pub fn working_items_per_minute(_speed: i32) -> i32 {
+    unimplemented!("Implement working_items_per_minute")
+}
+
+pub fn success_rate(_speed: i32) -> f32 {
+    unimplemented!("Implement success_rate")
+}