You're treating the contents of $row and $col as a sprintf format sequence. Change

printf " %s At ($row, $col) the row is %s and the column is %s for EUR
+ & NAM \n",
    $feedback_value, $my_row, $my_column;
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to

printf " %s At (%s, %s) the row is %s and the column is %s for EUR & N
+AM \n",
    $feedback_value, $row, $col, $my_row, $my_column;
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If you wanted to to interpolate the values into the format string because you were using the same format string over and over again, you'd need to convert instances of "%" to "%%".

my $power = '95%';

(my $escaped_power = $power) =~ s/%/%%/g;
my $fmt = "sample: %-4s  result: %5.2f  power: $escaped_power\n";

for (0..$#data) {
    printf($fmt, $_, $data[$_]);
}
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