how to write if and else in twig code example

Example 1: twig if else

// twig if else
{% if process_1 %}
   {{ process_1 }}
{% elseif process_2 %}
   Only {{ process_2 }} left!
{% else %}
   Sold-out!
{% endif %}

Example 2: twig if statement

{% if temperature > 18 and temperature < 27 %}
    <p>It's a nice day for a walk in the park.</p>
{% endif %}