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Loops/Increment loop index within loop body: Difference between revisions
Loops/Increment loop index within loop body (view source)
Revision as of 10:21, 22 August 2019
, 4 years agoAdd Racket
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Line 2,380:
n = 41 49,752,014,150,467
n = 42 99,504,028,301,131</pre>
=={{header|Racket}}==
Racket's <code>for</code> doesn't allow modification of index on the fly. The usual idiom for writing this kind of loop is to use named let, as shown here.
<lang racket>#lang racket
(require math/number-theory)
(define (comma x)
(string-join
(reverse
(for/list ([digit (in-list (reverse (string->list (~a x))))] [i (in-naturals)])
(cond
[(and (= 0 (modulo i 3)) (> i 0)) (string digit #\,)]
[else (string digit)])))
""))
(let loop ([x 42] [cnt 0])
(cond
[(= cnt 42) (void)]
[(prime? x) (printf "~a: ~a\n" (add1 cnt) (comma x))
(loop (* 2 x) (add1 cnt))]
[else (loop (add1 x) cnt)]))</lang>
{{out}}
<pre>
1: 43
2: 89
3: 179
4: 359
5: 719
6: 1,439
7: 2,879
8: 5,779
9: 11,579
10: 23,159
11: 46,327
12: 92,657
13: 185,323
14: 370,661
15: 741,337
16: 1,482,707
17: 2,965,421
18: 5,930,887
19: 11,861,791
20: 23,723,597
21: 47,447,201
22: 94,894,427
23: 189,788,857
24: 379,577,741
25: 759,155,483
26: 1,518,310,967
27: 3,036,621,941
28: 6,073,243,889
29: 12,146,487,779
30: 24,292,975,649
31: 48,585,951,311
32: 97,171,902,629
33: 194,343,805,267
34: 388,687,610,539
35: 777,375,221,081
36: 1,554,750,442,183
37: 3,109,500,884,389
38: 6,219,001,768,781
39: 12,438,003,537,571
40: 24,876,007,075,181
41: 49,752,014,150,467
42: 99,504,028,301,131
</pre>
=={{header|REXX}}==
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