Don't test what you just set

Say you're looking for the first card that's 7 or more, and want to print it if it's there.

A common way to write this sets a "found" flag when you find the card, leaves the loop, and then tests the flag afterwards to work out how the loop ended.

cell  contents  notes
 10      030    INP 30  cells 10-14: read cards until one is 7 or more, or a negative one ends them
 11      130    CLA 30
 12      317    TAC 17
 13      731    SUB 31
 14      310    TAC 10
 15      133    CLA 33  cells 15-16: found: set the flag and leave the loop
 16      632    STO 32
 17      132    CLA 32  cells 17-20: after the loop, test the flag
 18      320    TAC 20
 19      530    OUT 30
 20      900    HRS 00
 30      000
 31      007
 32     -001    the flag: -1 not found, 0 found
 33      000

Step through the natural way in Cardigan

But at the moment you find the card, you already know you found it: the loop's own test just told you. So do the work right there and skip the flag entirely. Whenever you're about to set something and then jump to a test of it, jump straight to the answer instead.

cell  contents  notes
 10      030    INP 30  cells 10-16: read cards until one is 7 or more, or a negative one ends them
 11      130    CLA 30
 12      316    TAC 16
 13      731    SUB 31
 14      310    TAC 10
 15      530    OUT 30  found: act on it here, where the loop's own test already said so
 16      900    HRS 00
 30      000
 31      007

Step through the CARDIAC way in Cardigan

Both print 9. The flag version takes 15 cells and runs 21 instructions; acting on the spot takes 9 cells and runs 17.

From the tips in cardiac-code on GitHub. All the tips.