Why does "1" in awk print the current line?

Question

In this answer,

awk '$2=="no"{$3="N/A"}1' file

was accepted. Note the 1 at the end of the AWK script. In the comments, the author of the answer said

[1 is] a cryptic way to display the current line.

I'm puzzled. How does that work?

Answer 1

In awk,

Since 1 always evaluates to true, it performs default operation {print $0}, hence prints the current line stored in $0

So, awk '$2=="no"{$3="N/A"}1' file is equivalent to and shorthand of

awk '$2=="no"{$3="N/A"} {print $0}' file

Again $0 is default argument to print, so you could also write

awk '$2=="no"{$3="N/A"} {print}' file

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In-fact you could also use any non-zero number or any condition which always evaluates to true in place of 1