how make addition from 2 variable twig?

Question

Anyone knows how to addition two variable in twig I want to do something like:

{{ var1 }} + {{ var2 }}

Answer 1

Just do it inside the {{ }}

{{ var1 + var2 }}

If you want to assign it to some other variable:

{% set foo = var1 + var2 %}
{{ foo }}

Answer 2

Declaration :

{% set counter = 0 %}

Doing the addition :

{% set counter = counter + 1 %}

For displaying in twig template :

{{ counter }}