An operator is a symbol that tells the compiler to perform a specific arithmetic or logical operation. It usually forms an expression together with the operands. We often see it participating in mathematical operations or logical operations. PHP also contains many operators. This article explains in detail the very important comparison operators.
Comparison operator types
As their name implies, allow comparison of two values. The comparison operators are as follows:
1) $a > $b is greater than: if $a is strictly greater than $b, then TRUE is returned
2) $a 3) $a >= $b Greater than or equal to: If $a is greater than or equal to $b, return TRUE
4) $a 5) $a $b is not equal to: if $a is not equal to $b, return TRUE
6) $a != $b is not equal to: if $a is not equal to $b, return TRUE (same as above )
7) $a == $b is equal to: If $a is equal to $b, return TRUE
8) $a === $b is equal to: if $a is equal to $b, and their types are also the same, then Return TRUE
9) $a !== $b is not equal to: If $a is not equal to $b, or their types are different, then TRUE is returned
Among them, we need to focus on distinguishing between "equal to" and "all equal to", $a == $b only performs a comparison operation on the values of the two variables, while equality requires comparing the values and data types of the expressions on both sides of the operator at the same time. Only when the values on both sides are equal, the operation result will be is true". Combined with the "inequality" operator, for example, $a = 2; var_dump($a!==2); this expression returns "false" because 2 is equal to 2. In addition, $a = 2; is an integer type and 2 in var_dump($a!==2); is also an integer type, but the operator is not exactly equal to "!==", so the result is false, because 2 is equal to 2 . On the other hand, if this is the case $a = 2; var_dump($a!=='2'); the result of the operation is "true", because 2 is not equal to '2', and the following '2' is a string of '2' ', that is, not all equals not only compare the variable values, but also compare the data types of the variables.
Comparing results of different types in PHP
If the PHP comparison operator compares an integer and a string, the string will be converted to an integer and then compared. If you compare two numeric strings, they are compared as integers, and this rule also applies to switch statements.
For example:
var_dump(0 == "a"); // Return TRUE, "a" is converted to 0
var_dump("1" == "01"); // Return TRUE, treated as an integer
string Or comparison between null and string: Convert NULL to "" to compare numbers or strings
Comparison between bool or null: Convert to bool, FALSE Object built-in classes can define their own comparisons, different classes cannot Comparison, if the same class compares attributes
Comparison between string, resource or number: Convert strings and resources into numbers, compare according to ordinary mathematics
Comparison between arrays: Arrays with fewer members are smaller, if the operand 1 is in The key does not exist in operand 2, so the arrays cannot be compared and need to be compared value by value (see the following code)
Comparing array with any other type: array is always larger
Comparing object with any other type: object is always larger
Array comparison code:
function standard_array_compare($op1, $op2) { if (count($op1) < count($op2)) { //具有较少成员的数组较小 return -1; // $op1 < $op2 } elseif (count($op1) > count($op2)) { return 1; // $op1 > $op2 } foreach ($op1 as $key => $val) { if (!array_key_exists($key, $op2)) { return null; } else if ($val < $op2[$key]) { return -1; } elseif ($val > $op2[$key]) { return 1; } } return 0; // $op1 == $op2 }
Ternary operator in comparison operator:
Expression (expr1) ? (expr2) : (expr3) When the value of expression expr1 is TRUE, the value is expr2, when The expression expr1 evaluates to FALSE when it evaluates to expr3.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。


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