Welcome to Cars Assemble on Exercism’s Julia Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Comparison operators

Comparison operators in Julia are similar to many other languages, though with some extra options for math-lovers.

For equality, the operators are == (equal) and != or ≠ (not equal).

txt = "abc"
txt == "abc"  # true
txt != "abc"  # false
txt ≠ "abc"  # false (synonym for !=)

In addition, we have the various greater/less than operators.

1 < 3  # true
3 > 3  # false
3 <= 3  # true
3 ≤ 3  # true (synonym for <=)
4 >= 3  # true
4 ≥ 3  # true (synonym for >=)

As often with Julia, an appropriate editor makes use of the mathematical symbol easy. Type \ne, \le or \ge then TAB to get ≠, ≤ or ≥.

The previous example uses only numbers, but we will see in other parts of the syllabus that various additional types have a sense of ordering and can be tested for greater/less than.

Comparison operators can be chained, which allows a clear and concise syntax:

n = 3
1 ≤ n ≤ 5  # true (n "between" two limits)

The previous example is a synonym for 1 ≤ n && n ≤ 5.

Branching with `if`

This is the full form of an if statement:

if conditional1
    statements...
elseif conditional2
    statements...
else
    statements...
end

There is no need for parentheses () or braces {}, and indentation is “only” to improve readability (but readability is very important!).

Both elseif and else are optional, and there can be multiple elseif blocks. However, the end is required.

It is possible to nest if statements, though you might want to help readability with the thoughtful use of parentheses, indents and comments.

The shortest form of an if statement would be something like this:

if n < 0
    n = 0
end

As a reminder: only expressions that evaluate to true or false can be used as conditionals. Julia deliberately avoids any concept of “truthiness”, so zero values, empty strings and empty arrays are not equivalent to false.

Ternary operator

A simple and common situation is picking one of two values based on a conditional.

Julia, like many languages, has a ternary operator to make this more concise.

The syntax is conditional ? value_if_true : value_if_false.

So the previous example could be rewritten:

n = n < 0 ? 0 : n

Parentheses are not required by the compiler, but may improve readability.

Instructions

In this exercise you will 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. Each of the required functions takes a single integer parameter, the speed of the assembly line.

1. Calculate the success rate

Implement the success_rate() method to calculate the probability 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.

julia> success_rate(10)
0.77

2. Calculate the production rate per hour

Implement the production_rate_per_hour() method to calculate the assembly line’s production rate per hour, taking into account its success rate.

julia> production_rate_per_hour(6)
1193.4

Note that the value returned is floating-point.

3. Calculate the number of working items produced per minute

Implement the working_items_per_minute() method to calculate how many working cars are produced per minute:

julia> working_items_per_minute(6)
19

Note that the value returned is an integer: incomplete items are not included.

Source

Created by

@colinleach

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Cars Assemble