Commodore 64 User Manual page 135

STOP
This statement will halt program execution. The message, BREAK IN
xxx will be displayed, where xxx is the line number containing STOP. The
program may be restarted by using the CONT command. STOP is nor-
mally used in debugging a program.
SYS
SYS is followed by a decimal number or numeric value in the range
0-65535. The program will then begin executing the machine language
program starting at that memory location. This is similar to the USR
function, but does not allow parameter passing.
WAIT
WAIT is used to halt the program until the contents of a memory loca-
tion changes in a specific way. WAIT is followed by a memory location
(X) and up to two variables . The format is:
WAIT X,Y,Z
The contents of the memory location are first exclusive-ORed with the
third number, if present, and then logically ANDed with the second
number. If the result is zero, the program goes back to that memory
location and checks again. When the result is nonzero, the program
continues with the next statement.
NUMERIC FUNCTIONS
ABS(X ) (absolute value)
ABS returns the absolute value of the number, without its sign (+ or
-). The answer is always positive.
ATN(X) (arctangent)
Returns the angle, measured in radians, whose tangent is X.
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