Pointers on C

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1、lastmodified:2011.06.051AQuickStart1.1IntroductionItisalwaysdifficulttostartdescribingaprogramminglanguagebecauselittledetailsdonotmakemuchsenseuntiloneknowsenoughtounderstandthe ʺbigpicture.ʺ Inthischapter,Itrytogiveyouaglimpseofthebigpicturebylookingatasampleprogramandexplainin

2、gitsworkingslinebyline.ThissampleprogramalsoshowsyouhowfamiliarproceduresareaccomplishedinC.ThisinformationplustheothertopicsdiscussedinthechapterintroduceyoutothebasicsoftheClanguagesothatyoucanbeginwritingusefulprograms.Theprogramwedissectreadstextfromthestandardinput,modifiesi

3、t,andwritesittothestandardoutput.Programl.lfirstreadsalistofcolumnnumbers.Thesenumbersarepairsandindicaterangesofcolumnsintheinputline.Thelististerminatedwithanegativenumber.Theremaininginputlinesarereadandprinted,thentheselectedcolumnsfromtheinputlinesareextractedandprimed.Notet

4、hatthefirstcolumninalineisnumberzero.Forexample,iftheinputis491220-1abcdefghijklmnopqrstuvwxyzHellothere,howareyou?Iamfine,thanks.Seeyou!Byethentheprogramwouldproduce:Originalinput:abcdefghijklmnopqxstuvwxyzRearrangedline:efghijmnopqrstu2Chapter1AQuickStartOriginalinput:Hellother

5、e,howareyou?Rearrangedline:otherhowareOriginalinput:Iamfine,thanks.Rearrangedline:fine,thanks.Originalinput:Seeyou!Rearrangedline:you!Originalinput:ByeRearrangedline:TheimportantpointaboutthisprogramisthatitillustratesmostofthebasictechniquesyouneedtoknowtobeginwritingCprograms./

6、***Thisprogramreadsinputlinesfromstandardinputandprints**eachinputline,followedbyjustsomeportionsoftheline,to**thestandardoutput.****Thefirstinputisalintofcolumnnumbers,whichendswitha**negativenumber.Thecolumnnumbersarepairedandspecify**rangesofcolumnsfromtheinputlinethataretobep

7、rinted.**Forexample,031012-1indicatesthatonlycolumns0through3**andcolumns10through12willbeprinted.*/#include#inc1ude#include#defineMAX_COLS20/*max#ofcolumnstoprocess*/#defineMAX_INPUT1000/*maxlenofinput&outputlines*/intread_column_numbers(intcolumns[]

8、,intmax);voidrearrange(char*output,charc