Billjk - 1 year ago 101

Ruby Question

I'm learning ruby, and there has been a bit of talk about the

`upto`

Example:

`grades = [88,99,73,56,87,64]`

sum = 0

0.upto(grades.length - 1) do |loop_index|

sum += grades[loop_index]

end

average = sum/grades.length

puts average

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Answer Source

Let's try an explanation:

You define an array

```
grades = [88,99,73,56,87,64]
```

and prepare a variable to store the sum:

```
sum = 0
```

`grades.length`

is 6 (there are 6 elements in the array), `(grades.length - 1)`

is 5.

with `0.upto(5)`

you loop from 0 to 5, `loop_index`

will be 0, then 1...

The first element of the array is `grades[0]`

(the index in the array starts with 0).
That's why you have to subtract 1 from the number of elements.

```
0.upto(grades.length - 1) do |loop_index|
```

Add the loop_index's value to sum.

```
sum += grades[loop_index]
end
```

Now you looped on each element and have the sum of all elements of the array.

You can calculate the average:

```
average = sum/grades.length
```

Now you write the result to stdout:

```
puts average
```

This was a *non-ruby-like* syntax. Ruby-like you would do it like this:

```
grades = [88,99,73,56,87,64]
sum = 0
grades.each do |value|
sum += value
end
average = sum/grades.length
puts average
```

Addendum based on Marc-AndrĂ©s comment:

You may use also `inject`

to avoid to define the initial sum:

```
grades = [88,99,73,56,87,64]
sum = grades.inject do |sum, value|
sum + value
end
average = sum / grades.length
puts average
```

Or even shorter:

```
grades = [88,99,73,56,87,64]
average = grades.inject(:+) / grades.length
puts average
```

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