[2. Basics of Delphi grammar] 4 Object Pascal operators and expressions

4.Object Pascal Operators and expressions

Operation is the processing and processing of data , Operators are symbols that operate on values of various data types in code .

stay Object Pascal in , Operators are divided into ： Monocular operator and binocular operator .

An expression is an operation formula that represents an evaluation rule , Constants are separated by operators and parentheses 、 Variable 、 function 、 Object and other operands .

4.1 Arithmetic operators and arithmetic expressions

1. Arithmetic operator

Object Pascal The arithmetic operator in ：

Operator	name	Example	Operator	name	Example
+	Correct	+a	Div	Divide the whole number by	a Div b
-	Take the negative	-b	Mod	Seeking remainder	a Mod b
*	ride	a*b	+	Add	a+b
/	except	a/b	-	reduce	a-b

• The operation result is automatically converted to high precision ;

• Division operations / Whether integer or real , The results are all real ;

• Div and Mod The operand of must be an integer , The result is an integer ;

2. The precedence of arithmetic operators

Operator	priority
+ Correct 、- Take the negative	1
*、/	2
Div、Mod	3
+、-	4

The same level operation is performed from left to right , Right parenthesis in expression , Calculate the expression in parentheses first , If there are multiple brackets , First calculate the expression in the inner bracket .

3. Arithmetic expressions

accord with Object Pascal The specified arithmetic expression should consider three aspects ： grammar 、 priority 、 type . Let's give an example of ：

for example ：

The mathematical formula	Arithmetic expressions
x/(yz)	x/(y*z)
(2x-y)/x	(2.0*x-y)/x
lg4.5+0.3ln4.5	log10(4.5)+0.3*ln(4.5)
(5x^2.3+3)/(3/5)	(5*Power(x, 2.3)+3.0)/(3.0/5.0)

4.2 Logical operators and Boolean expressions

4.2.1 Logical operators

Logical operators include ： Boolean operator 、 Bitwise operators and relational operators .

1. Boolean operator

Boolean operators can only operate on Boolean operands , The result is Boolean . Basic Boolean operators ：

• NOT “ Not ” Operator

  Calculate the opposite number of operands , Monocular operator .

  x	NOT x
  True	False
  False	True

• AND “ And ” Operator

  Only if both operands are True when , The result of the operation is True.

  x	y	x AND y
  False	False	False
  False	True	False
  True	True	True
  True	Flase	False

• OR “ or ” Operator

  As long as one of the two operands is True, The result of the calculation is True.

  x	y	x OR y
  False	False	False
  False	True	True
  True	True	True
  True	False	True

• XOR “ Exclusive or ” Operator

  When two operands are different, the result is True

  x	y	x XOR y
  Flase	False	False
  False	True	True
  True	True	False
  True	False	True

2. An operator

Bit operation is to perform operations on the binary bits of integer operands ,“ position ” Refers to binary bits , Bitwise operation means that adjacent operation results are not considered , Only the corresponding bits in the two operands are calculated .

An operator

The operator	give an example	Functional specifications
NOT	NOT x	take x Each binary bit of is negated , namely 1 Turn into 0,0 Turn into 1.
AND	x AND y	And the corresponding bits of the two operands , A fellow 1 The result is 1
OR	x OR y	Or the corresponding bits of two operands , A fellow 0 The result is 0
XOR	x XOR y	XOR the corresponding bits of two operands , When the corresponding bit is different, it is 1
SHL	x SHL y	take x The binary bit of moves to the left y position , Move left 1 A bit is a ride 2
SHR	x SHR y	take x The binary bit of moves to the right y position , Move right 1 Bit is equivalent to dividing 2

Example ：

x	y	operation	result
00100011		NOT x	11011100
00100011	11101110	x AND y	00100010
00100011	11101110	x OR y	11101111
00100011	11101110	x XOR y	11001100
124=11111100	2	x SHL y	11111000
124=11111100	2	x SHR y	01111110

3. Relational operator

Relational operators are used to compare the values of two data of the same type , The result is Boolean .

Relational operator

Relational operator	operation	Operand type
=	be equal to	Simple type 、 character string 、 Variable type 、 class 、 Class reference 、 The pointer 、 Collection types
<>	It's not equal to	Simple type 、 character string 、 Variable type 、 class 、 Class reference 、 The pointer 、 Collection types
<	Less than	Simple type 、 character string 、 Variable type
>	Greater than	Simple type 、 character string 、 Variable type
<=	Less than or equal to	Simple type 、 character string 、 Variable type 、 Collection types
>=	Greater than or equal to	Simple type 、 character string 、 Variable type 、 Collection types

Relational operation of set type ： hypothesis A and B It's two sets , be ：

• if A and B The elements of are exactly the same , be A=B by True, otherwise A<>B by True;

• if A Any element of is also B The elements of , be A<=B by True, said A yes B Subset ;

• if B Any element of is also A The elements of , be A>=B by True, said B yes A Subset ;

4.2.2 Boolean expression

Boolean expressions consist of Boolean operators and operands of boolean type . Boolean expressions can be used to describe complex judgment conditions .

for example ： To describe whether a real number is in an interval [10,100] Inside , Then Boolean expression ：

(x >= 10.0) and (x <= 100.0)

To describe whether a real number is in an interval [10,100] outside , Then Boolean expression ：

(x < 10.0) or (x > 100.0)

4.3 String operators

Object Pascal String operator for ：+, Used to connect two or more strings .

Format of string expression ：

< String expressions > + {< character string >|< character >}

Example ：

'Hello world' + '!'    //  The result is 'Hello world!'
'Delphi' + ' Programming '    //  The result is 'Delphi Programming '
'12 3' + '4' + '5' + 'abc' + 'xyz'   //  The result is '12 345abcxyz'

4.4 Operator precedence

In addition to the above operators , And pointer operators 、 Set operators 、 Class operators and address taking operators （ We will learn these gradually in the following content ）, All operators have priority ,Object Pascal The priority of the operator in the ：

priority	Operator	describe
1	@、NOT、+、-	Monocular operator
2	*、/、DIV、MOD、AND、SHL、SHR	Multiplication, division and some logical operators
3	+、-、OR、XOR	Add, subtract, and or operators
4	=、<>、<、>、<=、>=、in、is	Relationship 、 Set members and type comparison operators

Some of the above operators are not learned so far , In the following chapters, we will gradually learn .