Why does PHP convert String to Integer?

Question

I would like to know on what condition PHP decides when to convert from String to Integer and the other way around

Example:

$key = 0;
$test = \'test         


        

Answer 1

From the PHP Manual:

a variable's type is determined by the context in which the variable is used. That is to say, if a string value is assigned to variable $var, $var becomes a string. If an integer value is then assigned to $var, it becomes an integer.

See Type Juggling and Type Comparison Table and String conversion to numbers for details:

If the string does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the string will be evaluated as an integer. In all other cases it will be evaluated as a float.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.

And the chapter on Strings:

An integer or float is converted to a string representing the number textually (including the exponent part for floats). Floating point numbers can be converted using exponential notation (4.1E+6).

And also (was already given by deceze though) the chapter on Comparison Operators:

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.