The special characters can be used in QGIS expressions likewise in the MS Office package, where we have the option for inserting symbols and choosing the one we need.
With the principle of QGIS expressions, this particular task might be tricky, because we need to know the special character code and apply it to our formula. The total value of 65535 characters available in QGIS is overwhelming, but everyone should know the symbols, which are the most necessary on a daily basis. Because there is not much information about this matter I would like to list some of them. The general matter has been discussed in this article. All the elements & symbols will stick to my current working situation (Latin alphabet), but in the whole spectrum of characters, every language in the World has been considered.
KEYBOARD
char(033) - ! char(034) - " char(035) - # char(036) - $
char(037) - % char(038) - & char(039) - ' char(040) - (
char(041) - ) char(042) - * char(043) - + char(044) - ,
char(045) - - char(047) - / char(048) - 0 char(057) - 9
char(058) - : char(059) - ; char(060) - < char(061) - =
char(062) - > char(063) - ? char(064) - @ char(065) - A
char(090) - Z char(091) - [ char(092) - \ char(093) - ]
char(094) - ^ char(095) - _ char(096) - ` char(097) - a
char(122) - z char(123) - { char(124) - | char(125) - }
char(126) - ~ char(164) - ¤ char(166) - ¦ char(167) - §
char(168) - ¨ char(169) - © char(171) - « char(172) - ¬
char(174) - ® char(175) - ¯ char(177) - ± char(180) - ´
char(183) - · char(184) - ¸ char(187) - » char(191) - ¿
Conclusions:
Char(048-057) represents numbers between 0 and 9
Char(065-090) constitutes the English alphabet with capital (A – Z)
Char(097-122) constitutes the English alphabet with small letters (a-z)
Char(169) – copyright symbol
Char(174) – registered trademark ownership symbol
CURRENCIES
char(036) - $ char(162) - ¢ char(163) - £ char(164) - ¤ char(165) - ¥
SUPERSCRIPT & POWER
char(170) - ª char(178) - ² char(179) - ³ char(185) - ¹ char(186) - º char(188) - ¼ char(189) - ½ char(189) - ¾
SYMBOLS
char(176) - ° char(181) - µ char(182) - ¶ char(198) - Æ char(215) - × char(216) - Ø char(222) - Þ char(247) - ÷
Conclusions
char(176) – the Celcius degree symbol
Other stuff will be soon