C++ Basics.ppt

1、C+ Basics,Programming,Introduction to C+,C is a programming language developed in the 1970s with the UNIX operating system C programs are efficient and portable across different hardware platforms C+ is an extension of the C language C programs should run in C+ C+ supports “object-oriented” programm

2、ing,General form of a C+ program,/Program description is first #include directives go next using namespace std; int main() constant declarations go here variable declarations go hereassignment statements go here return 0; ,General form of a C+ program,/simple program #include using namespace std; in

3、t main()/ constant declarationconst double Pi = 3.14159;/ variable declarationsdouble radius;double area;/ assignment statementscout radius;area = Pi * radius * radius;cout “Area : “ area endl;return 0; ,Syntax of the C+ Language,Reserved words (appear in blue in Visual C+) Reserved words have a spe

4、cial meaning in C+. The list of reserved words: asm, auto, bool, break, case, catch, char, class, const, continue, default, delete, do, double, else, enum, extern, float, for, friend, goto, if, include, inline, int, long, namespace, new, operator, private, protected, public, register, return, short,

5、 signed, sizeof, static, struct, switch, template, this, throw, try, typedef, union, unsigned, using, virtual, void, volatile, while,Syntax of the C+ Language,Identifiers (appear in black in Visual C+) An identifier is a name for variables, constants, functions, etc. It consists of a letter followed

6、 by any sequence of letters, digits or underscores Names are case-sensitive. The following are unique identifiers: Hello, hello, whoami, whoAMI, WhoAmI Names cannot have special characters in theme.g., X=Y, J-20, #007, etc. are invalid identifiers. C+ reserved words cannot be used as identifiers. Ch

7、oose identifiers that are meaningful and easy to remember.,Syntax of the C+ Language,Comments (appear in green in Visual C+) Comments are explanatory notes not compiled (i.e. no executable code is generated for comments) Comments are done in two ways: / A double slash starts a single line comment/*

8、A slash followed by an asterisk marks the start of a multiple line comment.It ends with an asterisk followed by a slash */,Syntax of the C+ Language,Compiler Directive: #include It refers to a header file of library functions or variables (e.g. input and output). When you compile your C+ program, th

9、e compiler reads in the contents of the file before compiling the rest of your program. The included file is compiled together with the program. There are two forms of #include: #include / for pre-defined files #include “my_lib.h“ / for user-defined files,Libraries,#include loads the code from the s

10、tandard libraries #include / new I/O library #include / old I/O library #include / standard functions #include / math functions #include / contains random funct #include / time functionusing namespace std; indicates that the new C+ libraries should be used. If this line is left out, then the old ios

11、tream library is loaded: #include ,Constant Declarations,Constants represent permanent values. Their values can only be set in the declaration:const double pi = 3.14159; They can make a program more readable and maintainableConstant declaration syntax: const = ;Examples: const double US2HK = 7.8; co

12、nst double HK2Yuan = 1.07; const double US2Yuan = US2HK* HK2Yuan;,Variable Declarations,A variable is best thought of as a container for a value with an address: Variable declaration syntax:; Examples:int nickel;int penny;A variable must be declared before it can be used.int main()x = 5; / illegal:

13、x was not declared,5342.23,1024,Variable Declarations,A variable can be initialized in a declaration:int x = 3; Several variables of the same type can be declared in the same declaration:double total_USD, area; A variable must have only one type. For example, a variable of the type int can only hold

14、 integer values.,Types of Variable Declarations,Simple C+ variable types: int integer (32-bit integer on the PC) (example: 1) short 16-bit integer (allows 32,767) long 32-bit integer (allows 2,147,483,647) float floating point number (allows about 7 digits of precision: 0.1234567) double double prec

15、ision float (allows about 15 digits of precision: 0.12345678901234) char a single character (example: y),BINARY DIGIT,Simple Number System,Decimal What is the maximum value a 3 decimal digit number can hold? 999,Binary What is the maximum value a 16-binary digit number can hold?one bit for sign 0: p

16、ositive (or zero) 1: negative +32767,Decimal base,# digits,# digits,Binary base,Memory Depiction,float y = 12.5; short Temperature = 32; char Letter = c; short Number;,Memory location,Assignment Statements,Assignment syntax:= ;Examples:int n, m, k; / declarationn = 5;m = 6 + (4 * 6);k = (n * 2) + m;

17、k = k / 2;,Assignment Statements,A variable must be assigned a value before it can be used. Variables are not automatically initialized in VC+. int x, y; / x declared, but not initialized/ x and y have random valuesy = x; / the random value in x assigned to yOnce a value has been placed in a variabl

18、e, it stays there until the program changes it.,Assignment Statements,int NewStudents = 6; int OldStudents = 21; int TotalStudents;TotalStudents = NewStudents + OldStudents ;,Assignment Statements,TotalStudents = NewStudents + OldStudents;OldStudents = TotalStudents;,Value1 = 10; Value2 = 20;int Hol

19、d = Value1;Value1 = Value2;Value2 = Hold;,Arithmetic Operators,Common Addition + Subtraction - Multiplication * Division / Mod % Note No exponentiation operator,Integer Division,Integer division produces an integer result It rounds down the result Examples 3 / 2 evaluates to 1 4 / 6 evaluates to 0 1

20、0 / 3 evaluates to 3,Mod,Produces the remainder of the division Examples5 % 2 evaluates to 112 % 4 evaluates to 04 % 5 evaluates to 4,Converting inches to feet and inches,63 inch = 5 foot 3 inch 5 = 63 / 12 3 = 63 % 12,Operators and Precedence,Which of the following is it equivalent to mx + b ? (m *

21、 x) + b m * (x + b) Operator precedence tells how to evaluate expressions Standard precedence order ( ) Evaluated first, if nested innermost done first * / % Evaluated second. If there are several, then evaluate from left-to-right + - Evaluate third. If there are several, then evaluate from left-to-

22、right,Operator Precedence,Examples1 + 2 * 3 / 4 - 5 = 1 + 1 - 5 = -32 * 4 / 5 + 3 * 5 % 4 = 6/5 + 15%4 = 1+3 = 43.0 * 3 / 4 = 9.0 / 4 = 2.25(1 + 3) * (2 + 4 * 6) * 3) / 2 + 2 = 4 * (26*3)/2 + 2 = 158,Standard Input/Output,cin - the standard input streamInput operator “” extracts data from input “str

23、eam” (the keyboard by default) skips over white spaces extracts only characters of the right form and performs automatic conversion to the type specified,Standard Input/Output,cout - the standard output stream Output operator “ id score; cout “Student ID: “ id “ score: “ score endl;,/ Convert inches

24、 to feet and inches / Input: inches / Output: feet and inches #include using namespace std; int main() / inches to feet conversion factor const int in2feet = 12; int inches; / number of inches int feet; / number of feet cout inches; / Convert inches to feet and inches feet = inches / in2feet; inches

25、 = inches % in2feet; cout feet “ feet “ inches “ inches “ endl;return 0; ,Assignment Conversions,A floating-point expression assigned to an integer object is always rounded down (truncated) An integer expression assigned to a floating-point object is converted to a floating-point value Example 1:flo

26、at y = 2.7;int i = 15;int j = 10;i = y; / i is now 2cout i endl;y = j; / y is now 10.0cout y endl;,Assignment Conversions,Example 2: int m, n; double x, y; m = 3; n = 2.5; / 2.5 converted to 2 and assigned to n x = m/n; / 3/2=1 converted to 1.0 and assigned to x n = x+m/2;/ m/2=1 : integer division/

27、 x+m/2 : double addition because x is double/ convert result of m/2 to double (i.e. 1.0)/ x+m/2=2.0/ convert result of x+m/2 to int (i.e. 2)/ because n is int,White Spaces,Extra blanks or tabs (white spaces) are ignored x=3; x = 3 ; Blank lines and comments are treated as white spaces Code can be in

28、dented in any way More than one statement can be on one line int x, y; x=3; y = 10; int z = x+y; A single statement can be continued over several lines cout feet “ feet and “ inches “ inches“ endl;,Good Programming Style,Place each statement on a line by itself (except long cout statements)x = m/n;

29、Use blank lines to separate sections of codeUse the same indentation for all statements in the same block of code . (“Format selection”, ALT-F8, will automatically fix indentation)int main()int x;x = 5; return 0;,Good Programming Style,Use meaningful identifier namesdouble area, sum, radius;Document

30、 each variable when it is declareddouble area; / area of the circledouble distance; / distance from top to bottomDocument each segment of code / Convert inches to feet and inches feet = inches / in2feet; inches = inches % in2feet;Document the beginning of the program with a header that tells the purpose of the program/ Convert inches to feet and inches,