Comma-Separated Lists of Expressions
The initialization and increment expressions can be comma-separated lists of expressions. The commas, as used in these expressions, are comma operators, which guarantee that lists of expressions evaluate from left to right. The comma operator has the lowest precedence of all C++ operators. The value and type of a comma-separated list of expressions is the value and type of the rightmost expression. The comma operator is often used in
for statements, where its primary application is to enable you to use multiple initialization expressions and/or multiple increment expressions. For example, there may be several control variables in a single
for statement that must be initialized and incremented.