From Creatures Wiki
ADDV is a CAOS command used to perform addition.
Syntax: ADDV X (variable) Y (number)
Adds Y to X, and stores the result in X. Equivalent to X = X + Y.
Increment a variable:
ADDV va02 1
Adapted from the basic interactive plant script, used to grow the plant:
doif pose lt 5 setv va00 pose addv va00 1 pose va00 endi