Page 96 - Programming Microcontrollers in C

Multidimensional Arrays 81

that has much the appearance of a function called sizeof. To deter­
mine the size of any variable, use the sizeof operator as follows:
a = sizeof array;

which will return the number of bytes contained in array[][] above.
There are several important different ways that you can use the
sizeof operator. First, the value of the return from sizeof is in
characters. The type of the return is called a type size_t. This special
type is usually the largest unsigned type that the compiler supports.
For the MIX compiler, it is an unsigned long. If you should want
the size of a type in your program, you should enclose the parameter in
parentheses. If you want the size of any other item, do not use the paren­
theses. One other item. If the sizeof operator is used in a module
where an array is defined, it will give you the size of the array as above.
If you should pass an array to a function, the array name degenerates to
a pointer to the array, and in that case, the return from the sizeof
operator would give you the size of a pointer to the array.
A common example program using two-dimensional arrays is to
determine the Julian date. The Julian date is simply the day of the
year. The following function is one that allows counting the number
of days that have passed in a year.
int month_days[2][13] = {
{0,31,28,31,30,31,30,31,31,30,31,30,31},
{0,31,29,31,30,31,30,31,31,30,31,30,31}};
int Julian_data(int month, int date, int year)
{
int i,leap;
leap = year%4==0 && year%100!=0 || year%400==0;
for(i=1;i<month;i++)
day += month_days[leap][i];
return day;
}

The declaration

int month_days[2][13] = {
{0,31,28,31,30,31,30,31,31,30,31,30,31},
{0,31,29,31,30,31,30,31,31,30,31,30,31}};