Detailed explanation of PHP string self-calculation and numerical calculation usage

When a string is treated as a numerical value, the result and type are as follows:

If the string does not contain '.', 'e' or 'E ' and its numeric value is within the range of integer types (defined by PHP_INT_MAX), the string will be evaluated as integer. In all other cases the value is treated as float.

The beginning of the string determines its value. If the string begins with a legal numeric value, that numeric value is used. Otherwise its value is 0 (zero). Legal values ​​consist of an optional sign, followed by one or more digits (possibly with a decimal point), and then an optional exponent part. The exponent part consists of an ‘e’ or ‘E’ followed by one or more digits.

The following will be converted into an integer:

[+/-][0-9][*]

The following will be converted into a floating point typenumber:

[+/-][0-9][.][0-9][e/E][0-9][*]

$r = '123' + 1;
var_dump($r);// 输出结果 int(124)$r = '123.4' + 1;
var_dump($r);// 输出结果 float(124.4)$r = '1.5e4' + 1;
var_dump($r);// 输出结果 float(15001)$r = '123456789123456789' + 1;
var_dump($r);// 输出结果 float(1.2345678912346E+17)$r = '123abc' + 1;
var_dump($r);// 输出结果 int(124)$r = '123e1abc' + 1;
var_dump($r);// 输出结果 float(1231)$r = '123.abc' + 1;
var_dump($r);//输出结果 float(124)$r = '+123abc' + 1;
var_dump($r);// 输出结果 int(124)$r = '-123abc' + 1;
var_dump($r);// 输出结果 int(-122)$r = 'abc' + 1;
var_dump($r);// 输出结果 int(1)

It has been determined that an integer is required ( floating point number), you can use intval() (floatval()) to first convert the string into an integer (floating point number), and then perform calculations with other values.

one. Addition of numeric strings in PHP

1. If the two strings do not have a valid value at the beginning or are not numeric strings, the two strings will be regarded as 0 when added;

$a="abc";
$b="b01";
$a+$b是0

2. When adding two numerical strings, the significant digits are added.

$a="100";
$b="01a";
$a+$b=101;

3/If the string contains ‘.’, ‘e’, ‘E’, it will be processed as a float type number.

$a="100";
$b="12.6a";
$a+$b=112.6;

$a='10';
$b='12.3e3';
$a+$b同样为float型float(12310)

Compare two strings in 2.php (< > ==);

Compare two strings in 1.php to see if they are equal, Generally, (==) is not used, because (==) will change the original data type , but use the strcmp(str1, str2) series of functions strcmp($str1,$str2);(strcmp It is forced to convert to string type for comparison).

$a='123';
$b='123.';($b后多了一个小数点)

But when compared with (==), the result is true

var_dump($a==$b);

So it is generally not used (= =) Compare strings.

In addition, when a number is compared with a string, the string will be converted to int or float type (numberic_string contains ‘.’, ‘e’, ‘E’).

‘abc’转化为int(0)；
‘12ab’转化为int(12);
‘12.3e3'转化为float(12300);

2. Comparison of (> <)

2-1: If it is a comparison of two strings, compare the ASCII codes of the corresponding characters one by one.

2-2: If numbers are compared with strings, the strings are first converted into numbers and then compared.

2-3: If two numeric strings (pure numeric strings) are compared, the two strings are first converted into numbers and then compared.

$a='100';
$b='20';
则$a>$b;

But

如$a=''100a;
$b='20';时，
结果为$a<$b;

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