C++语言学习第二章

Program Organization
C++ program Collection of definitions, declarations and functions Collection can span multiple files physically A files containing C++ code is called a translation unit Advantages Structured into small understandable units Complexity is reduced Overall program size decreases
Comments
Allow prose or commentary to be included in program Importance Programs are read far more often than they are written Programs need to be understood so that they can be maintained C++ has two conventions for comments // single line comment (preferred) /* long comment */ (save for debugging) Typical uses Identify program and who wrote it Record when program was written Add descriptions of modifications A program should at least include 20% comments.
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Integer Object Types
The basic integer object type is int An int is usually chosen to be the most efficient data type on the underlying hardware. The size of an int depends on the machine and the compiler On PCs it is normally 16 or 32 bits In Microsoft Visual C++ 2.0 and later it is 32 bits Other integers object types short: typically uses less bits long: typically uses more bits : sizeof(short) ≤ sizeof(int) ≤ sizeof(long) Signed and unsigned integer object type Signed integers are represented in two’s-complement form. The mostsignificant bit holds the sign: 1 for negative, 0 for positive and zero. Different types allow programmers to use resources more efficiently Standard arithmetic and relational operations are available for these types
Object
Object is a representation of some information Name Values or properties Data members Ability to react to requests (messages)!! Member functions When an object receives a message, one of two actions are performed Object is directed to perform an action Object changes one of its properties In C++ we usually say that a definition of the built-in data type (integer, float, double etc.) is object not variable. object,
A First Program – Hello world!
Preprocessor // Program: Display greetings directives // Author(s): Ima Programmer // Date: 1/24/2001 Comments #include <iostream> #include <string> Provides simple access using namespace std; Function int main() named { main() cout << "Hello world!" << endl; indicates return 0; start of } program Insertion Function Ends executions statement of main() whracter Object Types
Character type char is related to the integer types Characters are encoded using a scheme where an integer represents a particular character ASCII is the dominant encoding scheme Examples ' ' encoded as 32 '+' encoded as 43 'A' encoded as 65 'Z' encoded as 90 'a' encoded as 97 'z' encoded as 122 See appendix A for the complete ASCII character set We can always assume that ’a’ < ’b’ < ’c’ < ’A’ < ’B’ < ’C’ < ’0’ < ’1’ < ’2’ < the following relationships hold. … < ’z’ … < ’Z’ … < ’9’
Insertion Definitions Extraction
Definition with initialization
cout << "Area = " << Area << " = Length " << Length << " * Width " << Width << endl; return 0; }
Integer Constants
Integer constants are positive or negative whole numbers Integer constant forms Decimal Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 Octal (base 8) Digits 0, 1, 2, 3, 4, 5, 6, 7 Hexadecimal (base 16) Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F Examples L or l indicates long integer 234 31 102L 989L 056 031 077L 010L 0889 (illegal) 0x2A 0x45 0xffL 0xA1eL The range of represented number of integer object types: 16 bits integer: signed: –32768 ~ 32768 unsigned: 0 ~ 65535 32 bits integer: signed: –2147483647 ~ 2147483647 unsigned: 0 ~ 4294967295
Chapter 2 :
The Fundamentals of C++
Key Concepts:
function main() include comments definitions simple input and output integer, floating-point, and characters types integer, floating-point, and characters literals C++ names declarations expressions usual unary conversions usual binary conversions operator precedence operator associativity iostream insertion and extraction
Character Object Types
Arithmetic and relational operations are defined for characters types 'a' < 'b' is true '4' > '3' is true '6' <= '2' is false 'a'+1='b' Also in ASCII 'a'+1 = 'A'+1 = '2'+1 = '9'+1 = character encode set 'b' 'B' '3' ???