Lecture2:BeginningtoPrograminC++（C++编程入门）BeginningtoPrograminC++（C++编程入门）常量与变量Constants（常量）符号常量的定义注意：判断下列语句是否正确Variables（变量）ProgramExampleVariablesandAssignments变量1.变量的声明格式：数据类型变量名列表；如：inta;floatx,y;charch;intm=4,n=21;//声明时初始化charch=´A´;2.变量的赋值格式:：变量=表达式；如:：x=6;y=x+2;a=sqrt(b);y=x=x+2;IdentifiersForexampleKeywordsInitializingVariables注意：Simpleoutputtothescreen（简单的屏幕输出）OutputusingcoutExamplesUsingcoutIncludeDirectivesEscapeSequencesInputUsingcinReadingDataFromcinDesigningInputandOutputComments(注释)数据类型29说明：31注意：Datatypes(数据类型)DataTypesandExpressionsWritingIntegerconstantsWritingDoubleConstantsIntegertypesFloatingpointtypesTypecharcharconstantsTypeboolDatatypesizes(数据类型的大小)Operators（运算符）TheassignmentoperatorArithmeticoperatorResultsofOperatorsDivisionofDoublesDivisionofIntegersIntegerRemaindersArithmeticExpressionsCombinedassignmentoperatorsIncrementandDecrementOperatorsPreincrementWhentheoperatorisusedbeforethevariable(++cor–c)Variableischanged,thentheexpressionitisinisevaluated.PosincrementWhentheoperatorisusedafterthevariable(c++orc--)Expressionthevariableisinexecutes,thenthevariableischanged.Ifc=5,thencout<<++c;cischangedto6,thenprintedoutcout<<c++;Printsout5(coutisexecutedbeforetheincrement.cthenbecomes6WhenvariablenotinexpressionPreincrementingandpostincrementinghavesameeffect++c;cout<<c;andc++;cout<<c;arethesame逗号运算和逗号表达式Operatorprecedence(运算符的优先级)Typeconversionsandcasts(类型转换和强转)TypeCompatibilitiesintdouble(part1)intdouble(part2)charintboolintManualconversionProgrammingpitfallsProgrammingpitfallsProgrammingpitfallsQuicksyntaxreference