CJam, -17 bytes

r2e|i8,*

Try it online.

HQ9+, 2 bytes

QQ

outputs

QQQQ

I think it is not forbidden here.

Python 2.6, 10

print`-.1`

Prints -0.10000000000000001, which is 20 chars.

Note that the string repr shows more precision. print-.1 just gives -.1, and print.1/3 gives 0.0333333333333 for only 13 digits of accuracy.

Mathematica, 1 byte

#

Prints #1.

Python 2, 11

print`id`*1

Print the string representation of the built-in id, which is 22 chars:

<built-in function id>

The *1 is to get the code to 11 chars. You could also do print id;00.

More boring alternative 11's are:

print'1'*22
print 9**21

Matlab, 7 bytes

'a':'e'

Output:

The output contains newline ans = newline newline abcde newline, so 14 bytes.

JavaScript (ES6), 23 bytes - 25 = -2

(n=2)=>'x'.repeat(23*n)

Just for fun here's a quine version with a score of 27 bytes -25 =2

a=(n=2)=>`a=${a}`.repeat(n)

Pyth, -15 -16

-1 by Dennis

**N9?zvz2

Prints [input]*9 quote characters, or 2*9 if the input is empty.

Pyth, 1 byte

T

Prints 10. It's a built in variable that initializes to 10.

Recall, 17 bytes

................!

17 NOOPs. Then the debugger ! is invoked and dumps the memory to the console. The memory is empty, but the header is 34 bytes long:

-- STATE DUMP --
----------------

Try it here.

CJam, -9

q_,{i}{;2}?G*'X*

Explanation

• q_,

Reads the entire input and pushes it, then pushes the length.

• {i}{;2}?

If the length of the input is over zero, convert it to an integer. Otherwise, pop the input and push 2.

• G*

Pushes 16 (the program length), then multiplies it by 2 if there is no input, or by the input.

• 'X*

Pushes X and multiplies it by the top of the stack.

Macaroni 0.0.2, 23 chars

print tobase pow 32 9 2

Prints 32⁹ in binary, which happens to conveniently turn out to be 46 characters long (it's 1000000000000000000000000000000000000000000000), without a trailing newline.

C, 19

printf("%0.36f",0);

prints 0.000000000000000000000000000000000000 which is 38 bytes long.

gs2, -18 bytes

CP437: W↕0!↨.2

Hex dump: 57 12 30 21 17 2e 32

W reads numbers from STDIN into a list. ↕0 appends a 2 to the list, and ! extracts the first element. Then ↨. (the list [0,1,2,3,4,5,6]) is repeated (2) this many times.

This is very similar to Dennis's CJam answer -- gs2 just combines r and i into one byte.

Note: I had to fix a bug in the gs2 implementation for this to work: previously, each program had a hidden newline appended to its output, which was entirely unintentional. It only surfaced after I tried to solve this program (the language was designed for anarchy golf, which ignores trailing newlines in all problems), and I only pushed a fix to master just now, so feel free to take this answer with a grain of salt.

Perl, 27 bytes - 25 = 2

$n=pop||2;print"n"x($n*27);

Thanks to the excellent commentators for their help on this one :)

It produces 27 "n"'s multiplied by $n, which defaults to 2 if @ARGV is undefined.

dc, 10 - 25 = -15

2?A*Ar^1-n

Takes a blank line for "no input".

Calculates 10 ^ (10 * n) - 1, where n is the input, or 2 if input is empty. Prints a string of 9s of the required length.

• 2 push 2 to the stack in case input is empty
• ? push input to the stack
• A push 10 to the stack (dc has shortcuts A-F for 10 - 15)
• * pop twice and multiply (multiply input by 10)
• A push 10 to the stack
• r reverse top two stack elements
• ^ exponentiate 10 ^ (10 * input)
• 1- subtract 1 from the top of stack
• n print with no newline.

TI-Basic, 3 bytes

1ᴇ5

Prints 100000.

Julia, 42 bytes - 25 = 17

print("@"^42((r=readline())>""?int(r):2))

This reads a line from STDIN using readline(). If it's empty, i.e. no input has been provided, then n is defined to be the input converted to an integer. Otherwise n is 2. We then print 42​n @s to STDOUT.

JavaScript ES6, 33 - 25 = 8

(a=2)=>Array(a*33).fill(0).join``

dc, 19 - 25 = -6

2?19*[1n1-d0<l]dslx

Takes a number (2 is pushed to the stack as backup) and multiplies it by 19. Prints a 1 (no newline) and decrements the number. Loops while the number is greater than 0.

><>, 21 + 2 (-v flag) - 25 = -2 bytes

l0=?2f6+*v
-1o;?=0::<

test it here!

Thanks Cole for helping fix my errors

First checks the stack length, if it's 0 put 2 on the stack. Multiplies it by 21 (code length), then outputs the unicode representation of that number and decrements it by 1, loops until 0. (you'll have to inspect the output to see the characters, since the browser won't display them)

Perl, 18 - 25 = -7

print$=x(<>*9||18)

The special variable $=, a.k.a. $FORMAT_LINES_PER_PAGE, begins its life as 60, and therefore only needs to be duplicated half as many times as byte output needed.

Ruby, 24 - 25 = -1

$><<?x*24*(gets||2).to_i

q, 10 3 bytes

3#0

Outputs 6 bytes: "0 0 0\n".

JavaScript (ES6), 50-25=25

a=prompt();alert("0".repeat(48*(isNaN(a|0)?2:+a)))

Ruby, 6 bytes

p ?a*9

Prints "aaaaaaaaa" (including the quotes) and a newline.

Mouse, 21 bytes

1I:(I.43<^9!1I.+I:)$

Ungolfed:

1 I:                  ~ Begin a loop index at 1
( I. 43 < ^           ~ While I < 43...
  9 !                 ~ Print 9 to STDOUT
  1 I. + I:           ~ Increment I
)$

><>, 29 + 2 (-v flag) - 25 = 6

l0=?21-:0(?;fe+1-ao:0=f*e+0.~

Takes input on the stack, which I believe is populated through -v on the official interpreter. Prints newlines only.

Microscript, 1

0

Prints the digit 0, followed by a newline.

C++, 80 bytes

#include<iostream>
int main(){int i=0;while(i<20){std::cout<<&i;i++;}return 0;}

note the newline character is two characters. (if you don't want it to be, change i<20 to i<=19 to get back to the same byte count.)

Sample output (will change every time)

0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C0088FA0C

same 8 character memory address 20 times.

q (bonus), 27 bytes

1#[;"x"]27*2^first"J"$.z.x;