awk / gawk printf when variable format string, changing zero to dash - awk

Question

I have a table of numbers I am printing in awk using printf.
The printf accomplishes some truncation for the numbers.
(cat <<E\OF
Name,Where,Grade
Bob,Sydney,75.12
Sue,Sydney,65.2475
George,Sydney,84.6
Jack,Sydney,35
Amy,Sydney,
EOF
)|gawk 'BEGIN{FS=","}
FNR==1 {print("Name","Where","Grade");next}
{if ($3<50) {$3=0}
printf("%s,%s,%d \n",$1,$2,$3)}'
This produces:
Name Where Grade
Bob,Sydney,75
Sue,Sydney,65
George,Sydney,84
Jack,Sydney,0
Amy,Sydney,0
What I want is to display scores which are less than 50, or missing, as a dash ("-").
Name Where Grade
Bob,Sydney,75
Sue,Sydney,65
George,Sydney,84
Jack,Sydney,-
Amy,Sydney,-
This requires the 3rd string format in printf change from %d to %s.
So in some rows, the third column should be a value, and in some rows, the third column should be a string. How can I tell this to GAWK? Or should I just pipe through another awk to re-format?

Answer 1

$ gawk 'BEGIN{FS=","}
FNR==1 {print("Name","Where","Grade");next}
{if ($3<50) {$3="-"} else {$3=sprintf("%d", $3)}
printf("%s,%s,%s \n",$1,$2,$3)}' ip.txt
Name Where Grade
Bob,Sydney,75
Sue,Sydney,65
George,Sydney,84
Jack,Sydney,-
Amy,Sydney,-
use if-else to assign value to $3 as needed
sprintf allows to assign result of formatting to a variable
for this case, you could use int function as well
now printf will have %s for $3 as well
Assuming you missed the commas for the header and space after third column is not needed, you could do this with a simple one-liner
$ awk -F, -v OFS=, 'NR>1{$3 = $3 < 50 ? "-" : int($3)} 1' ip.txt
Name,Where,Grade
Bob,Sydney,75
Sue,Sydney,65
George,Sydney,84
Jack,Sydney,-
Amy,Sydney,-
?: ternary operator is alternate for if-else
1 is an awk idiom to print contents of $0