PHP type conversion, constants, system constants, magic constants, constants
PHP type conversion, constants, system constants, and magic Constants
1. Automatic type conversion;
During operation and judgment, automatic type conversion is performed; 1) convert other types to bool; 1) convert to boolean type conversion; 1) convert integer to boolean type conversion from 0 to false; convert non-0 to true; 2) convert null strings and '0' ("0") to false, convert others to true; 3) convert empty arrays to false, and convert non-empty arrays to true; 4) convert null to false 5) if the resource is not successfully opened, the value is 0 or null. If the resource is not opened successfully, convert the value to 'false' or '0'. 2) convert other types to strings (String concatenation ); null bool int float 1) convert null to null String (empty string not displayed) 2) convert integer directly to corresponding string 5 => '5'; 3) convert real number directly to corresponding string, but the end 0 is not converted (the last 0 decimal point of the real number); 4) true is converted to '1', false is converted to an empty string; string, Boolean, integer, floating point, null3) type conversion during operation 1) true/false to 1/0; 2) null to 0; 3) values starting with a string are converted to the corresponding values; 4) if the string starts with no value, it is directly converted to 0; (null, string, bool) <int <float
2. Forced type conversion
Is to manually convert a type value to another type value; 1. type conversion functions intval, strval, floatval $ num1 = 1.2; $ num2 = strval ($ num1 ); // convert the value of $ num1 to a string; var_dump ($ num1); var_dump ($ num2); 2. (type) $ variable cannot be converted to resource $ num2 = (unset) $ num2; convert to null 3. The settype (variable, type) type must be written as a string; change the type and value of the variable; Note 1) convert the floating point to an integer to directly remove decimal places; 2) echo (int) ($ num1 + 0.5); rounding
3. Constants
1) constant definition define (constant name, constant value) define ('song', 22); Note: 1) constant name is a string; 2) constant value must be a scalar 3) the constant name is generally in uppercase and different from the variable. 4) the constant name and variable name have the same naming rules. 2) system constant _ LINE _ current row number _ FILE _ current FILE name _ DIR _ current FILE directory; PHP_ OS operating system PHP_VERSION php version magic constant: __function _ FUNCTION name__ FUNCTION _ FUNCTION name; __class _ CLASS name _ METHOD _ NAMESPACE __: NAMESPACE _ NAMESPACE; 3) constant judgment defined (constant name) constant name must be a string; judge whether a constant has been defined;
4. Operators and expressions;
1) Arithmetic Operator +-(multiplication)/(Division) %. % modulo/remainder 0% 3 = 012% 10 = 25% 19 = 41% 3 = 1; 2% 3 = 2; 3% 3 = 0; -9% 4 =-19%-4 = 1; the result symbol of the modulo operation depends on the first number. Judge that the parity X % 2 = 0 is an even number, which can be divisible by X % 2! If it is set to 0, it is an odd number and cannot be divided into 2*3 = 8 exponent operations; 2 3 = 8; 3 2 = 9;
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