Initialization Rules for Arrays

C++ has several rules about initializing arrays. They restrict when you can do it, and they determine what happens if the number of array elements doesn’t match the number of values in the initializer. Let’s examine these rules.

You can use the initialization form only when defining the array. You cannot use it later, and you cannot assign one array wholesale to another:

int cards[4] = {3, 6, 8, 10};       // okay
int hand[4];                        // okay
hand[4] = {5, 6, 7, 9};             // not allowed
hand = cards;                       // not allowed

However, you can use subscripts and assign values to the elements of an array individually.

When initializing an array, you can provide fewer values than array elements. For example, the following statement initializes only the first two elements of hotelTips:

float hotelTips[5] = {5.0, 2.5};

If you partially initialize an array, the compiler sets the remaining elements to zero. Thus, it’s easy to initialize all the elements of an array to zero—just explicitly initialize the first element to zero and then let the compiler initialize the remaining elements to zero:

long totals[500] = {0};

Note that if you initialize to {1} instead of to {0}, just the first element is set to 1; the rest still get set to 0.

If you leave the square brackets ([]) empty when you initialize an array, the C++ compiler counts the elements for you. Suppose, for example, that you make this declaration:

short things[] = {1, 5, 3, 8};

The compiler makes things an array of four elements.