One, arithmetic operators
* *: is a power result cannot exceed a range when the exponent is a decimal, the base cannot be a negative number
%: The number of operands on both sides of the remainder is an integer, if not to intercept, to remove all the fractional parts
Note: When a string participates in an operation and needs to be converted to an integer, the value is zero if it cannot be converted to an integer, ' 2 ' +1=3 ' a ' +1=1
Second, numeric comparison operators
Greater than or equal: The result of the comparison is true or nonzero, false or 0
<=>: comparison operation $a <=> $b
When a is greater than B: The value is 1
When a is less than B: The value is-1
When a equals B: The value is 0
When using this operator, the operand is automatically converted to an integer, and the value of zero is not converted to an integer.
Note: Because the floating-point number is not accurate, do not compare the numbers with similar values.
Three, string comparison
Iv. string connection and repetition
. : The point is the connector $a = ' a '. ' B '-to ' AB '
In print, you can write print directly $a $b-the same as print $a. $b
X: Repeat (there are spaces before and after X, in order to be separated from the variable name) ' A ' x 5---' AAAAA '
Returns an empty string if the number of repetitions is less than 1
Four, logical operators
&& (and) | | (OR)! (not) XOR
This logical operator is left-to-right with the value of the Boolean type.
Five, assignment operators
$a +=1--is equivalent to $ A = $a +1
Can even wait: $a = $b =3---$a =3 $b =3
Vi. self-increasing self-reduction
++var--$var 2= $var 1 + + + $var 1 #这两种用法是不行的
1, can be used as a string of self-increment: $a = ' AZ '; $a + + becomes $a = ' ba '
2, can not be used as a string of self-subtraction: When $a--by the number operation, the string first converted to 0 and then self-subtraction
3, when there are numbers in the string, or non-alphabetic and numeric symbols (such as #[email protected]#$%^), the self-increment is first changed to 0 and then self-increment
Like ' ab$c ' we5a '
4, pre-increase: $b =++ $a # $a first increment in the assignment # $a =1 $b =++ $a; $a =2 $b =2
Post-increment: $b = $a + + # $a first assign and then increment # $a =1 $b = $a + +; $a =2 $b =1
Is the function of a connection: $a +=1, $b = $a; ==> $a +=1; $b = $a;
Eight, conditional operators
Three operands: evaluates the conditional expression first, and executes the question mark (? The following operation, which executes a colon when false (:) After the operation.
$result = $var = = 0? 14:7 #一般只用于简单的条件 too complex is not as good as if statement looks intuitive
Ix. Precedence of operators (precedence)
Self-increment self-reduction highest, single operand higher than multi-operand (that is, value, assignment, such as higher than plus minus), numeric operations > Comparison operations (greater than or equal to what, but greater than less than (<>) higher than equals (= =) and not equal (! =))
> Bitwise arithmetic > Assignment operation (=) > Logical operation
X. The binding nature (associativity)
Binding associativity: When more than one symbol in an expression is the same priority, which is the first, which is the calculation? Is the left (left-associative), or the right (right-associative)
Usually left-associative: first, left, then right.
Right binding: Except (* *), generally not seen at all
For a chestnut: $a = $b =1 #一起赋值
$a = $b +=1 #先算b加一 re-assigned to a
When precedence is not known, parentheses are added to resolve all issues
The Perl language Primer--2--perl operator