"You don't know what you're talking about!" cried Humpty Dumpty. "How many days are there in a year?"
"Three hundred and sixty-five," said Alice.
"And how many birthdays have you?"
"And if you take one from three hundred and sixty-five, what remains?"
"Three hundred and sixty-four, of course."
Humpty Dumpty looked doubtful. "I'd rather see that done on paper," he said.

7. Subroutine Library

INTERCAL provides several built-in subroutines to which control can be transferred to perform various operations. These operations include many useful functions which are not easily representable in INTERCAL, such as addition, subtraction, etc.

7.1 Usage

In general, the operands are .1, .2, etc., or :1, :2, etc., and the result(s) are stored in what would have been the next operand(s). For instance, one routine adds .1 to .2 and stores the sum in .3, with .4 being used to indicate overflow. All variables not used for results are left unchanged.

7.2 Available Functions

At the time of this writing, only the most fundamental operations are offered in the library, as a more complete selection would require prohibitive time and core to implement. These functions, along with their corresponding entry points (entered via DO (entry) NEXT) are listed below.

7.3 Automagical Inclusion of the System Library

The C-INTERCAL compiler will automatically include the system library if a DO (1xxx) NEXT statement is used, and if no (1xxx) labels are defined anywhere, where (1xxx) is a label in the 1000-1999 range, inclusive. This was not an INTERCAL-72 feature.