拓扑序列是无环有向图中所有顶点的一个线性序列，图中任意路径中的各个顶点在该图的拓扑序列中保持先后关系。对于图3-4所示的有向图，(39)不是其的一个拓扑序列。

图3-4　有向图

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By　using　MP3,　a　600M-byte　music　CD　can　be(70)to　50M　bytes　or　less.　It　can　be　streamed(downloaded　in　chunks)so　that　you　can　begin　listening　to　the　opening　bars　while　the(71)of　the　file　arrives　in　the　background.　And,　most　important,　MP3　music　files　retain　good　listening(72)that(73)compression　schemes　lacked.　That(74)of　features　makes　accessing　and　distributing　music　on　the　Web　practical　for　the　first　time.

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The following suggestions increase program's(73)and make them easier to(74):

  Use a standard indention technique, blank lines, form. feeds, and spaces.

  Insert plenty of comments into your code.

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In　C　language,(70)variables　have　to　be　defined　outside　of　any　function,　this(71)actual　storage　for　it.

when　a　string　constant　is　written　in　C　program,　the　eompiler　creates(75)of　characters　containing　the　characters　of　the　string,　and　terminating　it　with　"\0".