• PHP

$s = number_format($x * 100.0, 1) . '%';

• C

char s[7];
sprintf(s, "%.2lf%%", x * 100);

• C++

auto s = std::format("{.1f}%", x * 100);

• C#

string s = $"{x:p1}";

• D

string percent = format("%.1f%%", x * 100.0);

• Dart

var s = "${(x * 100).toStringAsFixed(1)}%";

• Elixir

s = "#{Float.round(x * 100, 1)}%"

• Fortran

write (*,'(F5.1,"%")') x*100.

• Go

s := fmt.Sprintf("%.1f%%", 100.0*x)

• Haskell

s = Numeric.showFFloat (Just 1) (100*x) "%"

• JS

const percentFormatter = new Intl.NumberFormat('en-US', {
  style: 'percent',
  maximumSignificantDigits: 3
});

const s = percentFormatter.format(x);

• JS

const s = Math.round (x * 1000) / 10 + '%'

• Java

String s = "%.1f%%".formatted(x * 100);

• Java

String s = format("{0,number,0.0%}", x);

• Java

NumberFormat f = getPercentInstance();
f.setMaximumFractionDigits(1);
f.setRoundingMode(HALF_UP);
String s = f.format(x);

• Java

String s = new DecimalFormat("0.0%").format(x);

• Lua

local s = (x-x%10^-3)*100 .."%"

• Lua

s = string.format("%.1f%%", x*100)

• Pascal

s :=format('%.1f%%', [100.0*x]);  

• Perl

my $s = sprintf '%.1f%%', $x * 100;

• Python

s = f"{x:.01%}"

• Python

s = '{:.1%}'.format(x)

• Python

s = '%.1f%%' % (x * 100)

• Python

s = format(x, '.1%')

• Ruby

s = "%.1f%%" % (100 * x)

• Rust

let s = format!("{:.1}%", 100.0 * x);