(programming) nil

cause (source or reason of an event or action)

a program (leaflet listing information about a play, game or other activity) / (broadcasting) a program (performance of a show or other broadcast on radio or television)

error

to make an error, to slip

(computing) program (to write code, to enter a program or other instructions into a computer); event schedule

(algebra) variable / (computing) variable

trial and error