Variable that traverses the for is not updated

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Variable that traverses the for is not updated

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#1 by (1 votes)
#2 by (0 votes)

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I am trying that when the for exterior% completes an iteration, the variable i is updated, in the way that is indicated in the if after the for internal ( if i+self.nGroups > n )

  for i in 0..n
    for j in 0..self.nGroups-1
      if i+j <= n
        puts "i=#{i} , j=#{j}"
        @competition_users[i+j].group = j+1
        puts @competition_users[i+j].group
        @competition_users[i+j].save
      end
    end
    if  i+self.nGroups > n
      i += 1
    else
      i += self.nGroups
    end
  end

For the values n=4 , nGroups=2 , unfortunately the output of the puts is the following:

     i=0 , j=0
     1
     i=0 , j=1
     2
     i=1 , j=0
     1
     i=1 , j=1
     2
     i=2 , j=0
     1
     i=2 , j=1
     2
     i=3 , j=0
     1
     i=3 , j=1
     2
     i=4 , j=0
     1

When what I expect is:

     i=0 , j=0
     1
     i=0 , j=1
     2
     i=2 , j=0
     1
     i=2 , j=1
     2
     i=4 , j=0
     1

Basically, the i index does not change when I perform i += self.nGroups

Let's see if anyone can explain why it is, or if they can advise me to do it in another way. Thanks

ruby-on-rails ruby

asked by Jorge Vela Plaza 27.07.2017 в 20:49

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2 answers

1

I fixed it, since Ruby does not allow change in the loops for of its iterators, so there is no alternative but to change the structure for while . Therefore the code would be as follows:

 i = 0 
 while (i <= n)
  for j in 0..self.nGroups-1
    if i+j <= n
      puts "i=#{i} , j=#{j}"
      @competition_users[i+j].group = j+1
      puts @competition_users[i+j].group
      @competition_users[i+j].save
    end
  end
  if  i+self.nGroups > n
    i += 1
  else
    i += self.nGroups
  end
end

And the exit is the one commented:

answered by 27.07.2017 в 21:46

C ++, execute binary from a byte array Doubt with xml and laravel

score 0 · Accepted Answer

The problem is that even if you write i within your if, it is overwritten to the value that follows the iteration, for example, consider this code:

for i in 0..3
  puts "i (inicio): #{i}"
  i += 2
  puts "i (+2): #{i}\n\n"
end

Result:

i (inicio): 0
i (+2): 2

i (inicio): 1
i (+2): 3

i (inicio): 2
i (+2): 4

i (inicio): 3
i (+2): 5

You can see that i actually changes after adding 2 , however its value is assigned again the beginning of the iteration.

Therefore you must use a different variable to take control of the cycle.