Separating two strings without a separating character
Just an extended note for the "quoting" techniques:

You can also pick one character of the alphabet (e.g. $a$) and interpret it as a space and use $aa$ for $a$:

 hello world  -&gt; helloaworld
 amazing spacing -&gt; aamaazingaspaacing


However it is easy to see that this approach can lead to ambiguities:

 a are doubled -&gt; aaaaare doubled 
                 --OK_DECODING   -&gt; a are doubled
                 --WRONG_DECODING-&gt; aa re doubled


These ambiguities can be avoided/ignored if we assume that the "special" character $a$ appears only in a well defined format and context.

Indeed this technique is still used for representing quotes or double quotes in well-known formats: e.g it is used for strings in the CSV format: every string is double quoted and the double quotes in a string are "doubled". 

 COLUMN 1 | COLUMN 2            | COLUMN 3
 42        | My name is "Nobody" | He said "To be or not to be" 
 43        | "Quote me"          | Charater " embedded


Are represented in CVS files as:

 42,"My name is ""Nobody""","He said ""To be or not to be"""
 43,"""Quote me""","Character "" embedded"


It is also used for single quotes in the SQL language:

 SELECT 'This is a quoted string: ''Hello world''!!!'


But more modern languages/formats usually prefer the escape technique (see Yuval's answer)