Expression: $x = a * (b + c) - d / e$

Operator precedence and parentheses give the evaluation order: $(b+c)$ first, then $a * (\dots)$, then $d/e$, then the subtraction, then the assignment.

Three-address code

t1 = b + c
t2 = a * t1
t3 = d / e
t4 = t2 - t3
x  = t4

Syntax tree of the expression (each internal node becomes one three-address instruction, bottom-up)

(i) Quadruples (op, arg1, arg2, result)

#	op	arg1	arg2	result
0	+	b	c	t1
1	*	a	t1	t2
2	/	d	e	t3
3	-	t2	t3	t4
4	=	t4		x

(ii) Triples (op, arg1, arg2): there is no result field; a result is referred to by the number of the triple that computed it.

#	op	arg1	arg2
(0)	+	b	c
(1)	*	a	(0)
(2)	/	d	e
(3)	-	(1)	(2)
(4)	=	x	(3)

(iii) Indirect triples: the triples are the same as above, but a separate instruction list holds pointers to them. The order of execution can then be changed by reordering the pointers without touching the triples.

Instruction list	Points to
100	(0)
101	(1)
102	(2)
103	(3)
104	(4)

Triple #	op	arg1	arg2
(0)	+	b	c
(1)	*	a	(0)
(2)	/	d	e
(3)	-	(1)	(2)
(4)	=	x	(3)

Comparison

Form	Temporaries in symbol table	Easy to reorder for optimization
Quadruples	Yes (explicit result names)	Yes
Triples	No	No (numbers refer to positions)
Indirect triples	No	Yes (reorder the pointer list)