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Group: repetitive control
topics >
computer science >
programming >
foreach and for all statements
Topic:
for loop
Topic:
iterator
Topic:
generalized repetition
Topic:
multiple for loop
Topic:
quantified repetition
Topic:
simple loop
recursion
Topic:
termination of control unit
Summary
Repetition along with sequence and selection are the fundamental control structures. Repetition statements have an initialization section, iterated variables, and a termination condition. Pratt argues that loop control should identify its function, e.g., search or sequence generation, separately from the statements controlled. Jackson selects one form of repetition, a simple loop or for-all, to simplify program structure.Repetition can sometimes be replaced by recursion or simplified with a sentinel. For instance tail-recursion is equivalent to a simple loop. (cbb 5/80)
Subtopic: loop variables
Quote: a social machine occurs when people perform repeatable actions with repeatable results that can fail to meet standards [»holtAW_1997]
Subtopic: historical examples
Quote: the loop control computation should be clearly identified [»pratT3_1978] Quote: specify loops with initialization, incrementation, termination tests, and alternative paths [»pratT3_1978, OK] Quote: repetitive control requires some way to record state; uses a invocation parameter that acts as a named constant [»redeDH7_1979] Quote: del control primitive for APL; e.g., x.del.1000 repeats x 1000 times [»vanbFH12_2001]
Subtopic: foreach loops
Quote: Babbage developed 'backing' to reexecute a set of cards any number of times [»menaLF10_1842, OK] Quote: a Jaquard-loom with backing could weave symmetric and regular patterns with fewer cards Quote: subroutines for the assembly of repetitive programs; like structured programming, but seldom used [»wilkMV_1951]
Subtopic: while vs. repeat
Quote: in a 1975 study, most loops generated or scanned a list, vector, or string [»pratT3_1978]
Subtopic: testing and annotating loops
Quote: repeat..until is harder to use correctly since first iteration does not test the conditional; loop body has two distinct contexts [»jackMA_1975] Quote: in paper solutions with looping constructs, 75% had only a terminating condition [»paneJF2_2001] Quote: in paper solutions, 85% treated progress as all or nothing instead of counting [»paneJF2_2001]
Subtopic: initialization of loops
Quote: loops are the most error-prone structure; test 0, 1, 2, average, max-1, max, and max+1 iterations [»yamaT11_1998] Quote: in block schematic diagrams, annotate test arrows with the tested item or loop count
Subtopic: continue/break control
Quote: added 'init' predicate for guards; true only during the first execution of a loop [»parnDL8_1983]
Subtopic: loop exit
Quote: C's continue statement initiates the next iteration of the immediately enclosing loop [»ritcDM7_1978c] Quote: C's break statement terminates the immediately enclosing while, for, do, or switch [»ritcDM7_1978c]
Subtopic: loop termination with tagged values
Quote: loop exits can allow specialized terminations indicated by a label [»bochGV7_1973, OK]
Subtopic: avoid loops
Quote: reduce the number of orders by using tags instead of counting; e.g., use -1 to end a sequence of positive numbers [»wilkMV_1951]
Quote: all loops should have a fixed upper bound Quote: the relational model does not need iterative or recursive loops to extract information; few bugs and higher productivity [»coddEF_1990] QuoteRef: hamiM3_1976 ;;14 loops not allowed in HOS specification. Instead uses recursion with all variables unique and protected Quote: Hehner's 'if' statement is more robust than Dijkstra's 'do' because it fails if no guard is true, e.g., an unexpected state [»redeDH7_1979] Quote: can implement Dijkstra's 'do' statement via recursive calls of Hehner's 'if' statement Quote: in paper solutions, sets or subsets used for 95% of statements on multiple objects; 5% loops or iteration [»paneJF2_2001] Quote: prefer set and subset expressions over iterative operations; avoids loop counters, terminating flags, and current object
[»paneJF2_2001]
Topic: foreach and for all statements (16 items)
Topic: for loop (18 items)
Topic: iterator (13 items)
Topic: generalized repetition (16 items)
Topic: multiple for loop (2 items)
Topic: quantified repetition (11 items)
Topic: simple loop
(15 items)
Topic: recursion (16 items)
Topic: termination of control unit
(22 items)