C语言程序设计现代方法课件.ppt

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1、Chapter6Loops1Copyright©2008W.W.Norton&Company.Allrightsreserved.IterationStatementsC’siterationstatementsareusedtosetuploops.Aloopisastatementwhosejobistorepeatedlyexecutesomeotherstatement(theloopbody).InC,everyloophasacontrollingexpression.Eachtimetheloopbodyise

2、xecuted(aniterationoftheloop),thecontrollingexpressionisevaluated.Iftheexpressionistrue(hasavaluethat’snotzero)theloopcontinuestoexecute.Copyright©2008W.W.Norton&Company.Allrightsreserved.2IterationStatementsCprovidesthreeiterationstatements:Thewhilestatementisused

3、forloopswhosecontrollingexpressionistestedbeforetheloopbodyisexecuted.Thedostatementisusediftheexpressionistestedaftertheloopbodyisexecuted.Theforstatementisconvenientforloopsthatincrementordecrementacountingvariable.Copyright©2008W.W.Norton&Company.Allrightsreserv

4、ed.3ThewhileStatementUsingawhilestatementistheeasiestwaytosetupaloop.Thewhilestatementhastheformwhile(expression)statementexpressionisthecontrollingexpression;statementistheloopbody.Copyright©2008W.W.Norton&Company.Allrightsreserved.4ThewhileStatementExampleofawhil

5、estatement:while(i

6、uallyhasthevaluezero.Copyright©2008W.W.Norton&Company.Allrightsreserved.5ThewhileStatementAwhilestatementthatcomputesthesmallestpowerof2thatisgreaterthanorequaltoanumbern:i=1;while(i

7、now2.Isi

8、fmultiplestatementsareneeded,usebracestocreateasinglecompoundstatement:while(i>0){printf("Tminus%dandcounting",i);i--;}Someprogrammersalwaysuse