The Perl language Primer--2--perl operator

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

Seven, comma

Is the function of a connection: $a +=1, $b = $a; ==> $a +=1; $b = $a;

No eggs.

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