In C++11 you cannot use a range-based for loop to modify the contents of an array unless you declare the range variable as a reference variable.

Question

Quizplus · Accepted Answer

When using a range-based for loop with an array, the range variable is a copy of each element in the array by default. If you want to modify the contents of the array using a range-based for loop, you need to declare the range variable as a reference variable so that you can modify the original elements in the array. This behavior is a feature of C++11 and later versions.

In C++11 You Cannot Use a Range-Based for Loop to Modify