Introduction to PHP for Os X by Example
Basic Control Structures
- Comparison operators determine a true or false outcome in test expressions (==, !=, <, >, <=, >=).
- The unary not operator, !, can negate any expression (makes true false and false true).
- PHP (unlike Perl) has predefined Boolean values of true and false.
- The same comparison operators are used to compare both numbers and strings.
- String comparison is based on where the names would come when sorted in a list (Dictionary sort order).
- The if / elseif / else control structure is used to check if a series of conditions are true and to execute a block of code if one, other or none are true.
- Its best to check whether floating point numbers differ from one another by an acceptable threshold rather then using the equality operator.
- A while loop is used to loop over a block of code while a condition remains true.
- For short inline statements with a true/false outcome there’s a shorthand syntax:
(test equation)? [true result]: [false result]
- The for loop contains three expressions. The first is the initialization expression ($i) it is evaluated when the loop starts. The second is the test expression ($i>0) which is evaluated once each time through the loop. If its true the code block is executed if false the program moves on. The third is the iteration expression ($i–).
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