Nested Range-Based for Statements

To process the elements of a two-dimensional array, we use a nested loop in which the outer loop iterates through the rows and the inner loop iterates through the columns of a given row. Function printArray’s nested loop is implemented with range-based for statements. Lines 27 and 30 introduce the C++11 auto keyword, which tells the compiler to infer (determine) a variable’s data type based on the variable’s initializer value. The outer loop’s range variable row is initialized with an element from the parameter a. Looking at the array’s declaration, you can see that the array contains elements of type

so the compiler infers that row refers to a three-element array of int values (again, columns is 3). The const & in row’s declaration indicates that the reference cannot be used to modify the rows and prevents each row from being copied into the range variable. The inner loop’s range variable element is initialized with one element of the array represented by row, so the compiler infers that element refers to an int because each row contains three int values. In an IDE, you can typically hover your mouse over a variable declared with auto and the IDE will display the variable’s inferred type. Line 31 displays the value from a given row and column.