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385 lines
10 KiB
Text
385 lines
10 KiB
Text
<chapter id="language.operators">
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<title>Operators</title>
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<simpara>
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</simpara>
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<sect1 id="language.operators.arithmetic">
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<title>Arithmetic Operators</title>
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<simpara>
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Remember basic arithmetic from school? These work just
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like those.
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</simpara>
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<table>
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<title>Arithmetic Operators</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>example</entry>
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<entry>name</entry>
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<entry>result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>$a + $b</entry>
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<entry>Addition</entry>
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<entry>Sum of $a and $b.</entry>
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</row>
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<row>
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<entry>$a - $b</entry>
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<entry>Subtraction</entry>
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<entry>Remainder of $b subtracted from $a.</entry>
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</row>
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<row>
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<entry>$a * $b</entry>
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<entry>Multiplication</entry>
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<entry>Product of $a and $b.</entry>
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</row>
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<row>
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<entry>$a / $b</entry>
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<entry>Division</entry>
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<entry>Dividend of $a and $b.</entry>
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</row>
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<row>
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<entry>$a % $b</entry>
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<entry>Modulus</entry>
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<entry>Remainder of $a divided by $b.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<!-- This appears to be inaccurate. Division always returns a float.
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<simpara>
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The division operator ("/") returns an integer value (the result
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of an integer division) if the two operands are integers (or
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strings that get converted to integers). If either operand is a
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floating-point value, floating-point division is performed.
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</simpara>
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-->
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<sect1 id="language.operators.string">
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<title>String Operators</title>
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<simpara>
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There is only really one string operator -- the concatenation
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operator (".").
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</simpara>
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<para>
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<informalexample><programlisting>
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$a = "Hello ";
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$b = $a . "World!"; // now $b = "Hello World!"
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</programlisting></informalexample>
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</para>
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<sect1 id="language.operators.assignment">
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<title>Assignment Operators</title>
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<simpara>
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The basic assignment operator is "=". Your first inclination might
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be to think of this as "equal to". Don't. It really means that
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the the left operand gets set to the value of the expression on the
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rights (that is, "gets set to").
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</simpara>
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<para>
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The value of an assignment expression is the value assigned. That
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is, the value of "$a = 3" is 3. This allows you to do some tricky
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things: <informalexample><programlisting>
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$a = ($b = 4) + 5; // $a is equal to 9 now, and $b has been set to 4.
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</programlisting></informalexample>
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</para>
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<para>
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In addition to the basic assignment operator, there are "combined
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operators" for all of the binary arithmetic and string operators
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that allow you to use a value in an expression and then set its
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value to the result of that expression. For example: <informalexample><programlisting>
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$a = 3;
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$a += 5; // sets $a to 8, as if we had said: $a = $a + 5;
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$b = "Hello ";
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$b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!";
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</programlisting></informalexample>
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</para>
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<sect1 id="language.operators.bitwise">
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<title>Bitwise Operators</title>
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<simpara>
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Bitwise operators allow you to turn specific bits within an integer
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on or off.
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</simpara>
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<table>
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<title>Bitwise Operators</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>example</entry>
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<entry>name</entry>
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<entry>result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>$a & $b</entry>
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<entry>And</entry>
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<entry>Bits that are set in both $a and $b are set.</entry>
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</row>
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<row>
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<entry>$a | $b</entry>
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<entry>Or</entry>
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<entry>Bits that are set in either $a or $b are set.</entry>
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</row>
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<row>
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<entry>~ $a</entry>
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<entry>Not</entry>
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<entry>Bits that are set in $a are not set, and vice versa.</entry>
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</row>
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<row>
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<entry>$a << $b</entry>
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<entry>Shift left</entry>
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<entry>Shift the bits of $a $b steps to the left (each step means "multiply by two")</entry>
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</row>
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<row>
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<entry>$a >> $b</entry>
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<entry>Shift right</entry>
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<entry>Shift the bits of $a $b steps to the right (each step means "divide by two")</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<sect1 id="language.operators.logical">
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<title>Logical Operators</title>
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<table>
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<title>Logical Operators</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>example</entry>
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<entry>name</entry>
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<entry>result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>$a and $b</entry>
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<entry>And</entry>
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<entry>True of both $a and $b are true.</entry>
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</row>
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<row>
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<entry>$a or $b</entry>
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<entry>Or</entry>
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<entry>True if either $a or $b is true.</entry>
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</row>
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<row>
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<entry>$a xor $b</entry>
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<entry>Or</entry>
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<entry>True if either $a or $b is true, but not both.</entry>
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</row>
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<row>
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<entry>! $a</entry>
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<entry>Not</entry>
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<entry>True if $a is not true.</entry>
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</row>
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<row>
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<entry>$a && $b</entry>
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<entry>And</entry>
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<entry>True of both $a and $b are true.</entry>
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</row>
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<row>
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<entry>$a || $b</entry>
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<entry>Or</entry>
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<entry>True if either $a or $b is true.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<simpara>
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The reason for the two different variations of "and" and "or"
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operators is that they operate at different precedences. (See below.)
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</simpara>
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<sect1 id="language.operators.comparison">
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<title>Comparison Operators</title>
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<simpara>
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Comparison operators, as their name imply, allow you to compare two
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values.
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</simpara>
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<table>
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<title>Comparson Operators</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>example</entry>
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<entry>name</entry>
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<entry>result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>$a == $b</entry>
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<entry>Equal</entry>
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<entry>True if $a is equal to $b.</entry>
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</row>
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<row>
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<entry>$a != $b</entry>
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<entry>Not equal</entry>
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<entry>True if $a is not equal to $b.</entry>
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</row>
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<row>
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<entry>$a < $b</entry>
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<entry>Less than</entry>
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<entry>True if $a is strictly less than $b.</entry>
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</row>
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<row>
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<entry>$a > $b</entry>
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<entry>Greater than</entry>
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<entry>True if $a is strictly greater than $b.</entry>
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</row>
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<row>
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<entry>$a <= $b</entry>
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<entry>Less than or equal to </entry>
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<entry>True if $a is less than or equal to $b.</entry>
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</row>
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<row>
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<entry>$a >= $b</entry>
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<entry>Greater than or equal to </entry>
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<entry>True if $a is greater than or equal to $b.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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Another conditional operator is the "?:" (or trinary) operator, which
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operates as in C and many other languages.
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<informalexample><programlisting>(expr1) ? (expr2) : (expr3);</programlisting></informalexample>
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This expression returns to <replaceable>expr2</replaceable> if
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<replaceable>expr1</replaceable> evalutes to true, and expr3 if
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<replaceable>expr1</replaceable> evaluates to false.
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<sect1 id="language.operators.precedence">
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<title>Operator Precedence</title>
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<para>
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The precedence of an operator specifies how "tightly" it binds
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two expressions together. For example, in the expression
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<literal>1 + 5 * 3</literal>, the answer is 16 and not
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18 because the multiplication ("*") operator has a higher precedence
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than the addition ("+") operator.
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<para>
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The following table lists the precedence of operators with the
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lowest-precedence operators listed first.
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<table>
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<title>Operator Precedence</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Associativity</entry>
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<entry>Operators</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>left</entry>
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<entry>,</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>or</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>xor</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>and</entry>
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</row>
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<row>
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<entry>right</entry>
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<entry>print</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>= += -= *= /= .= %= &= != ~= <<= >>=</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>? :</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>||</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>&&</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>|</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>^</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>&</entry>
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</row>
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<row>
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<entry>non-associative</entry>
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<entry>== !=</entry>
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</row>
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<row>
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<entry>non-associative</entry>
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<entry>< <= > >=</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry><< >></entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>+ - .</entry>
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</row>
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<row>
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<entry>left</entry>
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<entry>* / %</entry>
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</row>
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<row>
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<entry>right</entry>
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<entry>! ~ ++ -- (int) (double) (string) (array) (object) @</entry>
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</row>
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<row>
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<entry>right</entry>
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<entry>[</entry>
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</row>
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<row>
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<entry>non-associative</entry>
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<entry>new</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</chapter>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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-->
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