Phrase reversals: Difference between revisions
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attesor edoc esarhp lasrever
reversal phrase code rosetta
</pre>
=={{header|Fortran}}==
The key here is the ability via F90 to specify an array span, as A(''first'':''last'':''step'') where the ''step'' can be negative... This facility is not available for CHARACTER variables where only TEXT(''first'':''last'') is available - no ''step'' is accommodated. However, one can have an array of CHARACTER*1 variables, and as an array they can be rolled bidirectionally. For convenience in initialising such an array, EQUIVALENCE(TEXT,ATXT) means that a normal multi-character text literal can be assigned to TEXT via the DATA statement, rather than having to specify the ATXT elements one at a time.
By identifying the first and last character position of each word in TEXT (or equivalently, their indices in ATXT) and storing them in arrays IST and LST, the i'th word can be fingered via IST(i) to LST(i) and of course a DO-loop can step in either direction. <lang Fortran> PROGRAM REVERSER !Just fooling around.
CHARACTER*(66) TEXT !Holds the text. Easily long enough.
CHARACTER*1 ATXT(66) !But this is what I play with.
EQUIVALENCE (TEXT,ATXT) !Same storage, different access abilities..
DATA TEXT/"Rosetta Code Phrase Reversal"/ !Easier to specify this for TEXT.
INTEGER IST(6),LST(6) !Start and stop positions.
INTEGER N,L,I !Counters.
INTEGER L1,L2 !Fingers for the scan.
CHARACTER*(*) AS,RW,FW,RO,FO !Now for some cramming.
PARAMETER (AS = "Words ordered as supplied") !So that some statements can fit on a line.
PARAMETER (RW = "Reversed words, ", FW = "Forward words, ")
PARAMETER (RO = "reverse order", FO = "forward order")
Chop the text into words.
N = 0 !No words found.
L = LEN(TEXT) !Multiple trailing spaces - no worries.
L2 = 0 !Syncopation: where the previous chomp ended.
10 L1 = L2 !Thus, where a fresh scan should follow.
11 L1 = L1 + 1 !Advance one.
IF (L1.GT.L) GO TO 20 !Finished yet?
IF (ATXT(L1).LE." ") GO TO 11 !No. Skip leading spaces.
L2 = L1 !Righto, L1 is the first non-blank.
12 L2 = L2 + 1 !Scan through the non-blanks.
IF (L2.GT.L) GO TO 13 !Is it safe to look?
IF (ATXT(L2).GT." ") GO TO 12 !Yes. Speed through non-blanks.
13 N = N + 1 !Righto, a word is found in TEXT(L1:L2 - 1)
IST(N) = L1 !So, recall its first character.
LST(N) = L2 - 1 !And its last.
IF (L2.LT.L) GO TO 10 !Perhaps more text follows.
Chuck the words around.
20 WRITE (6,21) N,TEXT !First, say what has been discovered.
21 FORMAT (I4," words have been isolated from the text ",A,/)
WRITE (6,22) AS, (" ",ATXT(IST(I):LST(I):+1), I = 1,N,+1)
WRITE (6,22) RW//RO,(" ",ATXT(LST(I):IST(I):-1), I = N,1,-1)
WRITE (6,22) FW//RO,(" ",ATXT(IST(I):LST(I):+1), I = N,1,-1)
WRITE (6,22) RW//FO,(" ",ATXT(LST(I):IST(I):-1), I = 1,N,+1)
22 FORMAT (A36,":",66A1)
END</lang>
And the output is...
<pre>
4 words have been isolated from the text Rosetta Code Phrase Reversal
Words ordered as supplied: Rosetta Code Phrase Reversal
Reversed words, reverse order: lasreveR esarhP edoC attesoR
Forward words, reverse order: Reversal Phrase Code Rosetta
Reversed words, forward order: attesoR edoC esarhP lasreveR
</pre>
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