PHP Expressions

An expression is the basic building block of the language.
 Anything with a value can be thought of as an expression. 
Examples include:
By combining many of these basic expressions, you can
 build larger, more complex expressions.
Note that the echo statement we've used in numerous 
examples cannot be part of a complex expression because
 it does not have a return value. The print statement, on
 the other hand, can be used as part of complex expression
 -- it does have a return value. In all other respects, echo 
and print are identical: they output data.

Expressions are combined and manipulated using operators.

The control structures in PHP are very similar to those
 used by the C language. Control structures are used to 
control the logical flow through a PHP script. PHP's control 
structures have two syntaxes that can be used interchangeably. 
The first form uses C-style curly braces to enclose statement 
 blocks, while the second style uses a more verbose syntax 
that includes explicit ending statements. The first style is 
preferable when the control structure is completely within 
a PHP code block. The second style is useful when the 
construct spans a large section of intermixed code and 
HTML. The two styles are completely interchangeable, 
however, so it is really a matter of personal preference 
which one you use. 

The if statement is a standard conditional found in most languages.
 Here are the two syntaxes for the if statement:
if(expr) {            if(expr):
  statements            statements
} elseif(expr) {      elseif(expr):
  statements            statements
} else {              else:
  statements            statements
}                     endif;
The if statement causes particular code to be executed if
 the expression it acts on is true. With the first form, 
you can omit the braces if you only need to execute a 
single statement.