Able to use a variable within another variable's name? Ruby - ruby

So my goal is to be able to run through a "while" loop and in each iteration create a new variable that includes the "iteration count" within that variables name and stores it for later use outside of the loop. See below for more details.
NOTE: The code is clearly wrong in so many ways but I'm writing it this way to make it more clear? as to what I am trying to accomplish. Thanks for any input on how this is possible.
count = "4"
while count > "0"
player"#{count}"_roll = rand(20)
puts 'Player "#{count}" rolled: "#{player"#{count}"_roll}"'
count -= 1
end
My goal is then to be able to access the variables that were created from within the loop at a later part of the program like so (more or less)
puts player4_roll
puts player3_roll
puts player2_roll
puts player1_roll
The key being that these variables were A) created in the loop B) With names relying on another variables input, and C) accessible outside the loop for later use.
Hopefully my question came out clear and any input will be greatly appreciated. I'm very new to programming and trying to get my head wrapped around some more complex ideas. I'm not sure if this is even possible to do in Ruby. Thanks!

I think the best way is to use arrays or hashes, with arrays its something like this:
count = 0
array = []
while count < 4 do
array[count] = rand(20)
puts "Player #{count} rolled: #{array[count]}"
count += 1
end
array.each do |var|
puts var
end
You store the result in the array and then you loop trough it. If you want the result of the second iteration of the loop you do something like this:
puts array[1]
If you want to use Hashes there are some modifications you need to do:
count = 0
hash = {}
while count < 4 do
hash["player#{count}_roll"] = rand(20)
puts "Player #{count} rolled: #{hash["player#{count}_roll"]}"
count += 1
end
hash.each do |key, var|
puts var
end
If you want the result of the second iteration of the loop you do something like this:
puts hash["player1_roll"]

You could set the variable using instance_variable_set and reference it that way
instance_variable_set("#player#{count}_roll", rand(20))

Related

Simple program but so very stuck- Loops in Ruby

I have to write a program which asks the user to enter a number.
The program keeps on asking the user for a number until the user types 'Stop'
at which point the sum of the numbers that the user has entered should be printed.
I've tried many,many things and none of my ideas work.
This is what I have - but I can that it isn't correct. What am I doing wrong?
I've only used while loops and arrays
total_user_input = []
# As long as the user inputs a number, the program will keep putting Give me a number
# and then adding that number to the total_user_input array.
puts "Give me a number: "
while user_input = gets.chomp.to_i
#add the input to the array total_user_input
total_user_input.push(user_input.to_i)
puts "Give me a number: "
# If the user however types stop, then the loop is broken and we jump down to the
# sum bit - where all of the numbers in the total_user_input array are added together
# and printed. End of program!
if user_input == "stop"
break
end
sum = 0
total_user_input.each { |num|
sum += num
}
puts sum
end
The output isn't as it should be.
As others have identified the problems with your code let me suggest how you might reorganize it. Ruby provides many ways to execute loops but you many find it desirable to primarily relay on the method Kernel#loop and the keyword break. (As you will learn in time, loop is particularly convenient when used with enumerators.)
def sum_numbers
tot = 0
loop do
print 'Gimme a number: '
s = gets.chomp
break if s == 'Stop'
tot += s.to_i
end
tot
end
The keyword break can optionally take an argument (though why that is not mentioned in the doc I cannot say), in which case it (if a literal) or its value (if a variable or method) is returned by loop. Here one would generally see
break tot if s == 'Stop'
without the final line, tot. As the loop returns tot and that is the last calculation performed by the method, the method will return the final value of tot.
You could have instead written
return tot if user_input == 'Stop'
but I think most coders believe best practice dictates that one should not return from a method from within a loop (or from within nested loops) unless there is a good reason for doing so.
Some small points:
I used print rather than puts to that the user's entry will be shown on the same line as the prompt.
I used s (for "string") rather than user_input because it reduces the chance of spelling mistakes (e.g., user_imput), speeds reading, and (possibly a foible of mine), looks neater. True, s is not descriptive, but one only has to remember its meaning for three consecutive lines of code. Others may disagree.
You could write, break if s.downcase == 'stop' if you want, say, 'stop' or 'STOP' to have the same effect as 'Stop'.
'23O3'.to_i #=> 23 (that's an an oh, not a zero), so in real life you'd want to confirm that either 'Stop' or the string representation of a number had been typed.
This is how I would do this preferring to use loop do end syntax with a break when it should. Also added a bit more text so user knows what's happening.
total_user_input = []
puts 'Give me a number or "stop" to end: '
loop do
user_input = gets.chomp
total_user_input << user_input.to_i
puts "Give me a number: "
break if user_input.downcase == "stop"
end
puts "Total entered: #{total_user_input.inject(&:+)}" unless total_user_input.empty?
puts 'goodbye!'
Note these few things:
get.chomp.to_i will convert every input to integer. ("stop" or any non integer string will be 0)
Arrangement of the flow is quite messy.
total_user_input = []
puts "Give me a number: "
while user_input = gets.chomp.strip
total_user_input.push(user_input.to_i)
sum = 0
total_user_input.each { |num|
sum += num
}
puts sum
if user_input == "stop"
break
end
end
Hope you understand this.

How can I collect block values in Ruby without an iterator?

Here's some code:
i = 0
collection = []
loop do
i += 1
break if complicated_predicate_of(i)
collection << i
end
collection
I don't know in advance how many times I'll need to iterate; that depends on complicated_predicate_of(i). I could do something like 0.upto(Float::INFINITY).times.collect do ... end but that's pretty ugly.
I'd like to do this:
i = 0
collection = loop.collect do
i += 1
break if complicated_predicate_of(i)
i
end
But, though it's not a syntax error for some reason, loop.collect doesn't seem to collect anything. (Neither does loop.reduce). collection is nil at the end of the statement.
In other words, I want to collect the values of a loop statement without an explicit iterator. Is there some way to achieve this?
You could write
collection = 1.step.take_while do |i|
i <= 3 # this block needs to return *false* to stop the taking
end
Whatever solution you choose in the end, remember that you can always opt to introduce a helper method with a self-explanatory name. Especially if you need to collect numbers like this in many places in your source code.
Say you wanted to hide the intricate bowels of your solution above, then this could be your helper method:
def numbers_until(&block)
i = 0
collection = []
loop do
i += 1
break if yield i
collection << i
end
collection
end
collection = numbers_until do |i|
i > 3 # this block needs to return *true* to stop the taking
end
You could write
def complicated_predicate_of(i)
i > 3
end
1.step.with_object([]) { |i,collection| complicated_predicate_of(i) ?
(break collection) : collection << i }
#=> [1, 2, 3]

For loop... Forever

I have a for loop that I would like to have increment forever.
My code:
for a in (0...Float::INFINITY).step(2)
puts a
end
Output:
0.0
2.0
4.0
Etc. Always with "#{a}.0"
Is there any way to express infinity as an integer, so that the output does not have a .0 at the end without preforming any operations on the contents of the loop?
Addendum
Could you also explain how your loop works? I am trying to find the most efficient solution, because since this loop will be iterating infinity, a few milliseconds shaved off will improve the performance greatly.
Also...
I will accept the solution that takes to shortest time to run to 1000000
According to benchmark both #Sefan and the while loop answers take the same ammount of timeFruity the while loop answers take a bit shorter, with the for loop answers in second, but the multiple loop do answers take far longer.
Since the reason why is out of the scope of this question, I have created another question that addresses why some loops are faster than others (https://stackoverflow.com/questions/33088764/peddle-to-the-metal-faster-loop-faster).
You can use Numeric#step without passing a limit:
0.step(by: 2) { |i| puts i }
Output:
0
2
4
6
...
You can also build your own Enumerator:
step2 = Enumerator.new do |y|
a = 0
loop do
y << a
a += 2
end
end
step2.each { |i| puts i }
You can use while true for that:
puts a = 0
puts a+=2 while true
BTW,
Is there any way to express infinity as an integer
NO
require 'bigdecimal'
(0..BigDecimal('Infinity')).step(2).each{ |n| puts n }
OR
require 'bigdecimal'
for a in (0...BigDecimal::INFINITY).step(2)
puts a
end
This is what the loop method is designed for. loop has no condition for which to run. It will run indefinitely and the only way to exit is to use the keyword break. (or raise a StopIteration)
a = 0
loop { puts a += 2}
This loop will be infinite as there is no break specified.
break can be specified very similarly to how the other answers use the while condition if needed:
a = 0
loop do
puts a += 2
break if a > 1_000_000
end
This loop will now exit once the value of a exceeds 1M.
That being said #Stefan's answer is more efficient as it does not store this integral value or have to perform any additional assignment but rather the number is simply yielded from an Enumerator and discarded it afterwards. The usefulness of this becomes more a matter of your implementation and purpose for this loop.
Try this:
arr = [0]
arr.cycle(1000000) { |i| puts arr[0] +=2 }
If you want infinite loop, then, don't pass any parameter to cycle
arr = [0]
arr.cycle { |i| puts arr[0] +=2 }
a = [-2]
puts a.unshift(a.shift+2) while 'loop forever'

How to run a simple Ruby script

I would like to make a program that checks to see if the number you enter is an even number. Sort of like making a leap year program but for any number divisible by 2.
Something along the lines of:
num = gets.chomp
while num != 0
if (num%2) == 0
puts 'yess'
else
puts 'nooo'
end
end
I knows there's something easy that I need to change for it to run.
(btw I just started learning Ruby yesterday!)
There are two problems here.
First being something that others have put, you need to make sure you turn the input into an integer using ".to_i" on your num variable.
Secondly, this code puts you into an infinite loop since you are using a "while" loop.
Since the number is only input once, you get stuck in the "while" loop forever no matter what the input is. Basically, "num" never stops being not 0.
You'd be better off using an if..else statement. Something like:
num = gets.chomp.to_i
if num != 0
if (num%2) == 0
puts 'yess'
else
puts 'nooo'
end
else
puts "that's 0, dude"
end
Integers have two methods for this. They are even? and odd?.
You can use this in your if statement as so:
if num.even?
puts 'yess'
else
puts 'nooo'
end
However, an easier way to write this is with ternary expressions:
puts num.even? ? "yes" : "no"
However, make sure num is an Integer. Anything coming from gets will be a String. So, you should be doing num = gets.chomp.to_i. Anything that is not a number, like "h", will return 0.
"5".to_i #=> 5
"h".to_i #=> 0

Syntax for a for loop in ruby

How do I do this type of for loop in Ruby?
for(int i=0; i<array.length; i++) {
}
array.each do |element|
element.do_stuff
end
or
for element in array do
element.do_stuff
end
If you need index, you can use this:
array.each_with_index do |element,index|
element.do_stuff(index)
end
limit = array.length;
for counter in 0..limit
--- make some actions ---
end
the other way to do that is the following
3.times do |n|
puts n;
end
thats will print 0, 1, 2, so could be used like array iterator also
Think that variant better fit to the author's needs
I keep hitting this as a top link for google "ruby for loop", so I wanted to add a solution for loops where the step wasn't simply '1'. For these cases, you can use the 'step' method that exists on Numerics and Date objects. I think this is a close approximation for a 'for' loop.
start = Date.new(2013,06,30)
stop = Date.new(2011,06,30)
# step back in time over two years, one week at a time
start.step(stop, -7).each do |d|
puts d
end
The equivalence would be
for i in (0...array.size)
end
or
(0...array.size).each do |i|
end
or
i = 0
while i < array.size do
array[i]
i = i + 1 # where you may freely set i to any value
end
array.each_index do |i|
...
end
It's not very Rubyish, but it's the best way to do the for loop from question in Ruby
To iterate a loop a fixed number of times, try:
n.times do
#Something to be done n times
end
If you don't need to access your array, (just a simple for loop) you can use upto or each :
Upto:
2.upto(4) {|i| puts i}
2
3
4
Each:
(2..4).each {|i| puts i}
2
3
4
What? From 2010 and nobody mentioned Ruby has a fine for /in loop (it's just nobody uses it):
ar = [1,2,3,4,5,6]
for item in ar
puts item
end
['foo', 'bar', 'baz'].each_with_index {|j, i| puts "#{i} #{j}"}
Ruby's enumeration loop syntax is different:
collection.each do |item|
...
end
This reads as "a call to the 'each' method of the array object instance 'collection' that takes block with 'blockargument' as argument". The block syntax in Ruby is 'do ... end' or '{ ... }' for single line statements.
The block argument '|item|' is optional but if provided, the first argument automatically represents the looped enumerated item.

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