task3

task3.rb

def make_output(array)
	40.times { print "-"}
	puts "\n#{array.join(", ")}"
end

def generate_array
	array = []
	rand(10..20).times { array << rand(-10..10)}
	array
end

#it can be made easier but I don't understand..
#when i tried to make: array.map { |i| i = array.min if i.positive? } it makes all positive numbers in nil, why?
def rework_array(array, min)
	array.each_with_index do |item, index|
	  if array[index] > 0
	    array[index] = min
	  end
	end
end

array_start = generate_array
min = array_start.min
puts "Minimal element = #{min}"

make_output(rework_array(array_start, min))

#when i tried to make: array.map { |i| i = array.min if i.positive? } it makes all positive numbers in nil, why?

This is because Ruby is a language of expressions ;)
Ruby calculates every expression.

What do you think about the result of calculation in this case: array.min if i.positive? when I.positive? is TRUE an FALSE?

And you don't need: a = something, because value returned from the block will be given as the element of new array

And you've got nil not instead positive but instead negative numbers ;)