CC++：从基础语法到优化策略 (4).pdf

C/C+Program DesignCS205Week 4Content Arrays Array-style strings string-class strings Structures Unions EnumerationsArrayThe slides are based on the book Data TypesFundamental types Integer Typeboolshort,int,long Char Type:char Floating-point Type:float,doubleCompound typesArrayArray-style string String classStructureArrays An array is a data form that can hold several values,all of one typeone type To define:The type of value to be stored in each elementThe name of the arrayThe number of elements in the array must be an integer constant,such as 10 or a const value,MICROS,or a constant expressionSquare brackets Why?Arrays Some statements for an arrayDeclaring an arrayAssigning values to array elementsInitializing an array Run program example/arrayone.cpp-small arrays of integersNote that if you use the sizeof operator with an array name,you get the number of bytes in the whole arrayFirst element index is 0Error:if subscript is equal or greater than the number of elements Initialization Rules for Arrays Several rules about initializing arrays Able to Use the initialization form only when defining the array Use subscripts and assign values to the elements of an array individually Partially initialize an array,the compiler sets the remaining elements to zeroCannot Use initialization later Assign one array wholesale to anotherC+11 Array Initialization Rules in C+11Can drop the=signCannot convert from a floating-point type to an integer type(narrowing)Cannot assign int type to char type(Outside the range of a char)StringThe slides are based on the book Strings A string is a series of characters stored in consecutivebytes of memoryC-style(array)stringstring class library Store a stringin an array of char(C-style)The last character of every string is the null characterThis null character is written 0The character is with ASCII code 0It serves to mark the strings endStrings Using a double quoted stringCalled a string constant or string literalInclude the terminating null character implicitlyMake sure the array is large enough to hold all the charactersNote that a string constant(with double quotes”)is not interchangeable with a character constant(with single quotes )Example cstrinit.cppConcatenating String Literals C+enables to concatenate string literalsAny two string constants separated only by whitespace Run program exampleUsing Strings in an Array/strings.cpp-storing strings in an array Shortening a string with 0 Beware of memory overflow(Problem)Adventures in String Input Run program example/instr1.cpp-reading more than one stringThe cin technique is to use whitespacespaces,tabs,and newlines(0)to delineate a stringThe input string might turn out to be longer than the destination array(buffer)A white space causes a problemReading String Input a Line at a Time(solved)To solve the problem:Line-oriented input with getline()See program example/instr2.cpp-reading more than one word with getline()Two argumentsOther Forms of String Literals Beside char,we have more following typeswchar_tchar16_tchar32_tchar8_t /c+2a char8_t name=u8SUSTech”;/UINT8 example wstr.cppstring-class stringsThe slides are based on the book string class The ISO/ANSI C+98 Standard expanded the C+library Include the string header file:#include Run program example strtype1.cppInitialize a string object,in a similar way as a C-style stringUse cin to store keyboard input in a string objectUse cout to display a string objectUse array notation to access individual characters stored in a string object DifferencesTreat object as a simple variable,not as an arrayAllow the program to handle the sizing automaticallyC+11 String Initialization C+11 enables 4 kinds of initialization Array-style String class Assign one string object to another Array assignment Use the+and+=operatorsMore string Class Operations Three functions for array-style stringstrcpy():copy a string to a character array =strcat():append a string to a character array +=strlen():calculate the length of a character array *.size()See three operations in program example strtype3.cpp Conclusionsstring objects tends to be simplersimplerthan using the C string functionsstring objects tends to be more safesafethan that of the CMore on string Class I/O See length of string in program example strtype4.cpp The difference and problems of array-style stringstrlen()reaches a null characterstring object is automatically set to zero sizeArray-style string has fixed size of inputcin.getline(charr,20);/Array-style string getline(cin,str);/string classStructures,Unions and EnumerationsThe slides are based on the book Introducing Structures Why structures?Almost all previous types are those you can directly useA structure is a more versatile data form than an arrayA structure is a user-definable type The keyword struct make a new typeUsing a Structure in a Program How to create a structure?Where to place the structure declaration?Inside or outside of mainCan a structure use a string class member?YesAssignment:use a comma-separated list of values enclosed in a pair of bracesIn C+11,the=sign is optionalEmpty braces result in the individual members being set to 0 See assignment and member access in program example stracture.cppOther Structure Properties What actions you can do for structures?Pass structures as arguments(multiple)to a function Have a function use a structure as a return value(multiple)Combine the definition of a structure form with the creation of structure variables Have member functions in addition to member variables Run program example assgn_st.cpp Member-wise assignment:use the assignment operator(=)to assign one structure to another of the same typeMore Structure Properties:Array Arrays of Structures Create arrays whose elements are structures An examplegifts itself is an array,not a structuregifts0 is a structureUnions A union is a data format Can hold different data types but only one type at a time Can use two or more formats but neversimultaneously Save memory union Keyword make a new typeprogram example union.cppEnumerations The C+enum facility provides an alternative to const for creating symbolic constants(#define)enum spectrum red,orange,yellow,green,blue,violet;It makes spectrum the name of a new typeIt establishes the members as symbolic constants for the integer values 05 By default,enumerators are assigned integer values starting with 0 for the first enumerator,1 for the second enumerator,and so forth The assigned values must be integers enum Keyword make a new typeEnumerations What operations can you do for enumerations?Assign it using the member You can set enumerator values explicitly Assign other variables using it Typecast values within the range Beware of the value ranges for enumerations