Convert Between Percentages and Decimal

Question

^{I, uh....honestly can't believe we don't have this one yet.}

Challenge

Write two functions or programs that:

1. Convert from decimal to percentage
2. Convert from percentage to decimal

You may also write a single program that does both of the above.

Format

Percentages must be taken and returned with a percent sign. (In many languages, this means they will be strings.) They may be integers or floating point numbers.

Decimals are just floating point numbers.

You do not need to handle rounding errors involving very large or very small floating point numbers.

In cases where the numbers are integers (such as 56.0) you may return 56, 56., or 56.0. (This is intended to make I/O more flexible.)

Test Cases

    0.0% <-> 0.0
  100.0% <-> 1.0
   56.0% <-> 0.56
  123.0% <-> 1.23
  -11.0% <-> -0.11
-214.91% <-> -2.1491

Scoring

This is code-golf, so the shortest answer in each language wins. If you write two separate programs, add their sizes for your score.

Answer 1

Mathematica, 34+20=54

to Decimal

ToExpression@StringDrop[#,-1]/100&

to Percentage

ToString[100#]<>"%"&

Answer 2

Japt, 7 bytes

From percentage:

/L

Test it online!

To percentage:

*L+'%

Test it online!

Answer 3

Python 2, 59 bytes

This one does both.

lambda s:'%'in s and`float(s[:-1])/100`or`float(s)*100`+'%'

Try it online!

Single functions, score 27 + 28 = 55

Decimal to percent, 27 bytes

lambda s:`float(s)*100`+'%'

Try it online!

Percent to decimal, 28 bytes

lambda s:`float(s[:-1])/100`

Try it online!

Answer 4

Java, 45 bytes

-4 bytes thanks to musicman523.

From decimal, to percent:

a->new Float(a.split("%")[0])/100

To percent, from decimal:

a->a*100+"%"

Answer 5

Perl 6, 10 + 10 = 20 bytes

Decimal to percentage:

*×100~'%'

Percentage to decimal:

*.chop/100

Answer 6

Dyalog APL, 20 bytes

To percentages

'%',⍨100∘×

From percentages

.01×∘⍎¯1↓⊢

Try it online!

Answer 7

PHP, 62 bytes 61 bytes

Thanks @ckjbgames

$i=readline();echo strstr($i,'%')?(float)$i/100:($i*100).'%';

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Answer 8

Haskell 16+19 = 35 bytes

Percent to decimal:

(/100).read.init

Decimal to percent:

(++"%").show.(*100)

Answer 9

JavaScript (ES6), 20+12=32 bytes

To Decimal

p=>parseFloat(p)/100

To Percentage

d=>d*100+'%'

Answer 10

05AB1E, 8 bytes

From % to decimal

¨т/

Try it online!

And from decimal to %

т*'%«

Try it online!

Explanations

¨т/
¨   # Cut of last character
 т/ # Divide by 100 (I know. Very creative)

 т*'%«
 т*    # Multiply by 100
   '%« # Append '%'

Answer 11

Jelly, 5 + 5 = 10 bytes

% → number

ṖV÷ȷ2

Try it online!

number → %

×ȷ2”%

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Full program only.

Answer 12

Excel, 15 + 4 = 19 bytes

Assuming that the values to be converted are stored in field A1

Percentage to decimal

=NUMBERVALUE(A1)

Decimal to percentage

=A1%

Answer 13

Python 3, 81 77 74 bytes

def a(m):e=m.strip("%");f=float(e);return f/100if e!=m else str(f*100)+"%"

Try it online!

EDIT: Saved 4 bytes by removing some whitespace.
EDIT: Saved another 3 bytes by setting float(e) to a variable.

Answer 14

Python 3, 26 24 23 bytes + 27 bytes = 50 bytes

First program (% -> decimal)

float(input()[:-1])*.01

Second program (decimal -> %):

str(float(input())*100)+'%'

Rather similar to the other one. Pretty easy, too.

Answer 15

Python 2, 67 bytes

lambda x:`float(x.strip('%'))*[100,.01]['%'in x]`+['%','']['%'in x]

Try it online!

Answer 16

Python 3, 71 bytes

i=input()
print(float(i[:-1])/100if'%'in i else'%.2f%%'%(float(i)*100))

Try it online!

Answer 17

Retina, 77 bytes

^-?
$&00
\b%?$
00%$&
\.(..)
$1.
(....)\.(.*)%%
.$1$2
^(-?)0+\B|\B0+(%?)$
$1$2

Try it online! Link includes test cases. Requires and returns input with at least one digit before and after the decimal point. Explanation: The first stage inserts two leading zeros after any sign, while the second stage inserts two trailing zeros and a % sign before any % sign. (The \b is needed to stop the pattern matching twice for percentages.) The third stage then multiplies by 100. This results in the correct numerical value for floats converted into percentages, but percentages are now 10,000 times too big and now have a duplicated % sign, so the fourth stage corrects this. The final stage then trims leading and/or trailing zeros as necessary.

Answer 18

ES6, 34 bytes

n=>1/n?n*100+'%':n.slice(0,-1)/100

(Now works with 0.0 and 0%)

Try it online!

This works because 1/n is NaN if a "%" is present and NaN is like false.

(1/n with n = 0 is Infinity (not NaN) and Infinity is not considered false by JS)

Answer 19

perl 5: 24 bytes

From % to decimal: 8 bytes (7 + 1 for p flag)

$_/=100

Usage:

echo '-214.91%' | perl -pe '$_/=100'

Output:

-2.1491

From decimal to %: 16 bytes (15 + 1 for p flag)

$_*=100;$_.="%"

Usage:

echo -2.1491 | perl -pe '$_*=100;$_.="%"'

Output:

-214.91%

Answer 20

Haskell, 60 42 bytes

Decimal to percentage (21 bytes)

f x = show(x*100)++"%"

Percentage to decimal (21 bytes)

f x = read(init x)/100

Answer 21

,,,, score 19

Percent to decimal, 10 bytes

-1⇆⊣f100⇆÷

Explanation

Take 56.0% for example.

-1⇆⊣f100⇆÷

               implicit input                               ["56.0%"]
-1             push -1                                      ["56.0%", -1]
  ⇆            switch "56.0%" and -1                        [-1, "56.0%"]
   ⊣           pop -1 and "56.0%" and push "56.0"           ["56.0"]
    f          pop "56.0" and push 56.0 (convert to float)  [56.0]
     100       push 100                                     [56.0, 100]
        ⇆      switch 56.0 and 100                          [100, 56.0]
         ÷     pop 100 and 56.0 and push 56.0 / 100         [0.56]
               implicit output                              []

Decimal to percent, 9 bytes

100×s'%⇆+

Explanation

Take 0.56 for example.

100×s'%⇆+

               implicitly take input and convert to float    [0.56]
100            push 100                                      [0.56, 100]
   ×           pop 0.56 and 100 and push 100 * 0.56          [56.0]
    s          pop 56.0 and push "56.0" (convert to string)  ["56.0"]
     '%        push "%"                                      ["56.0", "%"]
       ⇆       switch "56.0" and "%"                         ["%", "56.0"]
        +      pop "%" and "56.0" and push "56.0%"           ["56.0%"]
               implicit output                               []