When the calling program passes arrays, the actual array and the formal array must have the same number of dimensions.

However, it is not necessary for the actual array and the formal array to have the same number of elements in each dimension. Some languages allow formal array parameters that do not specify the number of elements in each dimension. For example, ALGOL does not allow upper bounds to be specified for the dimensions in a formal array parameter specification; and Pascal allows formal array parameters, called schemata, that are incompletely specified. (Schemata are discussed under “Passing Parameters to Pascal Schemata” later in this section.) In these cases, the system assigns the formal parameter the same number of elements as the actual parameter at run time.

Even if the formal parameter specifies the number of elements in each dimension of an array, the actual parameter can have a different number of elements. The system does not issue an error or warning in these cases. If the actual parameter passes more elements than the formal parameter can receive, the system ignores the extra elements.