awk - ternary conditional expression not working - awk

Question

Input (sample)
=== account ===
title,altTitle,platform,url,
title,altTitle,platform,url,
title,altTitle,platform,url,
title,altTitle,platform,url,
title,altTitle,platform,url,
__collate-by-account.awk
#! /usr/bin/awk -f
#
# Group together lines (records) by account name
BEGIN { FS = ":" }
### generate headers ###
{s = $1}
{if (s != p)
print "\n\n=== ", s " ==="
}
{p = s}
### process records ###
# print field $2 to last field
{for (i = 2; i <= NF; ++i)
# {if (i!=NF) printf $i":"; else printf $i}
{ i != NF ? printf $i":" : printf $i }
}
{printf "\n"}
This part works as intended:
{if (i!=NF) printf $i":"; else printf $i}
Why doesn't this work:
{ i != NF ? printf $i":" : printf $i }
Getting the following errors:
awk: scripts/utils/metadata/__collate-by-account.awk:18: { i != NF ? printf $i":" : printf $i }
awk: scripts/utils/metadata/__collate-by-account.awk:18: ^ syntax error
awk: scripts/utils/metadata/__collate-by-account.awk:18: { i != NF ? printf $i":" : printf $i }
awk: scripts/utils/metadata/__collate-by-account.awk:18: ^ syntax error

Answer 1

Solution, thanks to #James Brown:
### process records ###
# print field $2 to last field
{for (i = 2; i <= NF; ++i)
{ printf "%s%s",$i,(i!=NF?":":"") }
}
{printf "\n"}
Explaination:
First off, note that printf can't be inside the ternary operator, neither the conditional expression to be evaluated (for obvious reasons) nor the resulting if-else expressions that will be executed after evaluation.
printf formats and prints the results
%s%s format specifiers, outputs or substitutes the next 2 arguments as strings:
https://www.gnu.org/software/gawk/manual/html_node/Format-Modifiers.html
https://en.wikipedia.org/wiki/Printf_format_string
$i simply output the field that's being looped over, see the above for-loop
(i!=NF?":":"")
output ":" if i is not equal to NF,
otherwise output empty string ""