ruby how read user input in scanf-style like in C++

Question

I am new in Ruby. I need to read from user input (n) numbers and in C++ i used this code

for(i=0;i<N;i++)
{
  scanf("%d",&array[i]);
}

this code read exactly (n) numbers separated by any white spaces (tabs, spaces, newlines).

How i can do this in ruby?

in Ruby I tried to do it like this

require 'scanf'
n = scanf("%d");
arr = Array.new()
n.times { arr << scanf("%d") }

but this code don't work when i intut string like this:

1   4    8

but works fine if i input this

1
4
8

Answer 1

Use String#scan

I'm not 100% sure that I know what you really want to do here. If you just want to scan a string for digits, you can use String#scan to do something like this:

digits = '1   4    8'.scan /\d+/
# => ["1", "4", "8"]

This will return an array of digits found in the string, and you can access your digits array with any Array or Enumerable method you like.

If you want to handle newlines as well as tabs or spaces, all you need to do is add the m flag for multi-line matching. For example:

digits = '1
          4 8'.scan /\d+/m
# => ["1", "4", "8"]

Answer 2

Have to admit in this instance I'm unable to make a program that is quite as compact as the C++ version. It seems in Ruby scanf does not work like the C++ version for IO streams, and for strings you will need to provide a block to achieve multiple scans per line.

So here's one solution:

a = Array.new
n = gets.to_i

while a.length < n
  gets.scanf("%d") { |d| a << d[0] }
end

The only problem you get here is if you request for example 3 numbers, and then the user inputs 10 numbers on one line, then a will contain all those 10 numbers. To fix it you can just always truncate the array after the loop is done:

a = a.take(n)

This solution will read n numbers from the input regardless of white space. The user can input them all on one line, or on separate lines, or a mix of both (which I assume was your original requirement).