Implicit conversion rules for PHP strings and increment/decrement operations on strings that contain letters

The implicit type conversion rules and the increment/decrement operators for strings in PHP have been blurred before, and are summarized today.

One, implicit conversion

Implicit type conversion rules for binary arithmetic operators (http://php.net/manual/zh/language.types.string.php)

Type of first operand	Type of second operand	Type conversions
Integral type	Floating point Type	Integer conversion to floating-point type
Integral type	String	The string is converted to a number, and if the string is converted to a floating-point type, the integral type is also converted to floating-point
Floating point Type	String	string conversion to floating-point type

A summary is floating point > Integer > String. For example:

Integer + floating point = floating point type

$a = n; $b = 1.5; $c = $a + $b; Var_dump ($c); Float 13.5

　

Integer + (non-numeric and. Starting with) string = integral type

$a = n; $b = ' hello1.5 '; $c = $a + $b; Var_dump ($c); int 12

Here $b converted from a string to an integral type and turned into 0.

Integer + floating-point number beginning with string = floating-point type

$a = n; $b = ' 1.5hello '; $c = $a + $b; Var_dump ($c); Float 13.5

$b automatically converted to float 1.5

Integer + integer number beginning with string = integer

$a = n; $b = ' 1hello '; $c = $a + $b; Var_dump ($c); INT 13

　　

Integer + floating-point numeric string = floating-point type

$a = n; $b = ' 1.5 '; $c = $a + $b; Var_dump ($c); Float 13.5

　　

Integer + (starting with.) string = floating-point or integral type

$a = n; $b = '. 5hello '; $c = $a + $b; Var_dump ($c); Float 12.5

$b converted into 0.5.

$a = n; $b = '. Hello '; $c = $a + $b; Var_dump ($c); int 12

$b not converted to float 0.0 but converted to int 0

　　

Integer + string containing uppercase E or lowercase e (must have mantissa in the format required to satisfy scientific notation) = floating-point type

$a = 1; $b = ' 1e3 '; $c = $a + $b; Var_dump ($c); Float 1001

　　

$a = 1; $b = ' 1e-3 '; $c = $a + $b; Var_dump ($c); Float 1.001

　　

Integer + hexadecimal digit string = integral type

$a = 1; $b = ' 0x10 '; $c = $a + $b; Var_dump ($c); int 17

　　

two, auto increment/decrement operator

Automatic increment of letters

Auto Increment	Results
A	"B"
"Z"	"AA"
"Spaz"	"SPBA"
"B9"	"C0"
"12"	"13"

Example 1: A letter is incremented, and the result is its next letter in the alphabet

$a = ' a '; Var_dump (+ + $a); String ' B ' (length=1)

Example 2:

$a = ' a '; var_dump (--$a); String ' A ' (length=1)

Example 3: "Z" or "Z" is incremented, it becomes "a" or "a", and the character to the left of the character is incremented (if the result of "a" or "a" is at the left of the string the first character, then also need to insert a "a" or "a" on its left)

$a = ' Z '; var_dump (+ + $a); String ' AA ' (length=2)

　　

Example 4:

$a = ' Z1 '; Var_dump (+ $a); String ' Z2 ' (length=2)

　

Example 5:

$a = ' Z9 '; Var_dump (+ $a); String ' aa0 ' (length=3)

　　

Example 6:

$a = ' B9 '; Var_dump (+ $a); String ' C0 ' (length=2)

　　

Example 7:

$a = ' Spaz '; Var_dump (+ $a); String ' SPBA ' (length=4)

　　

Example 8:

$a = ' BZ '; Var_dump (+ + $a); String ' Ca ' (length=2)

　　

Example 9:

$a = ' 1z '; Var_dump (+ + $a); String ' 2a ' (length=2)

　　

Example 10:

$a = ' *a '; Var_dump (+ $a); String ' *b ' (length=2)

　　

Example 11:

$a = ' *a* '; Var_dump (+ $a); String ' *a* ' (length=3)

　　

Example 12:

$a = ' A * '; Var_dump (+ + $a); String ' A * ' (length=2)

　　

　　

　　

　　

　　

　　

　

Implicit conversion rules for PHP strings and increment/decrement operations on strings that contain letters