Mandamus - 9 months ago 54

Ruby Question

Here's what I wrote to check if a number is prime or not

`print "Enter number : "`

num = gets.chomp

i = 1

boo = true

while (i<num)

if (i%num==0)

boo=true

end

i++

end

if (boo==true)

puts (num+"is a prime number")

else

puts (num+"is not a prime number")

end

This gives an error, how can I fix it?

The output from cmd prompt:

Answer

Some problems:

`++`

operator doesn't exist in Ruby, you can use`+= 1`

instead- your
`num`

is a string, you can make it a number with`to_i`

method, like`num.to_i`

- if the reminder of your number divided by a precedent number is zero you should set to false, not true
- if you start at 1 your number will result always prime

Anyway, in a more idiomatic Ruby you can write this code something like

```
print "Enter number : "
num = gets.chomp.to_i
prime = (2..num - 1).all? { |i| num % i != 0 }
if prime
puts "#{num} is prime"
else
puts "#{num} is not prime"
end
```