Whitespace is a term that refers to characters that are used for formatting purposes. In C++, this refers primarily to spaces, tabs, and (sometimes) newlines. The C++ compiler generally ignores whitespace, with a few minor exceptions. For example, all the 4 lines below mean the same thing −
cout<<"Hello"; cout << "Hello"; cout << "Hello" ; cout << "Hello";
The exceptions where C++ compiler takes whitespace in consideration is inside quotes and for operator detection. So whenever you put in a string, c++ takes note of the whitespace. For example,
"Hello world!" "Hello world!"
Both of these are different strings. Also when you use compound operators or any multi-character operator, you cannot put in space between. For example,
<< and < < are different. Similarly, += and + = are different, with the latter not being a valid expression.