sitepoint_day3_php variables, operators, and comments
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Notice the last two lines in particular. You can include the name of a variable right inside a text string, and have the value inserted in its place if you surround the string with double quotes instead of single quotes. This process of converting variable names to their values is known as variable interpolation. However, as the last line demonstrates, a string surrounded with single quotes will not interpolate the variable names it contains. Kevin Yank $testvariable = 'Three';TRANSCRIPT
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About the Author
Kevin Yank
Kevin began developing for the
Web in 1995 and is a highly
respected technical author. He
wrote Build your own
Database Driven Website using
PHP and MySQL, a practical step-by-step
guide published by SitePoint, and he's
co-author of the SitePoint Tech Times, a
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View all articles by Kevin Yank...
By: Kevin Yank
June 16th, 2010
Reader Rating: 9
Variables in PHP are identical to variables in most other programming languages. For the uninitiated, a
variable can be thought of as a name that’s given to an imaginary box into which any literal value may be
placed. The following statement creates a variable called $testvariable (all variable names in PHP
begin with a dollar sign) and assigns it a literal value of 3:
$testvariable = 3;
PHP is a loosely typed language. This means that a single variable may contain any type of data, be it a number, a string of text, or some other kind of
value, and may change types over its lifetime. So the following statement, if you were to type it after the statement above, assigns a new value to the
existing $testvariable. In the process, the variable changes type: where it used to contain a number, it now contains a string of text:
$testvariable = 'Three';
The equals sign we used in the last two statements is called the assignment operator, as it’s used to assign values to variables. Other operators may be
used to perform various mathematical operations on values:
$testvariable = 1 + 1; // Assigns a value of 2
$testvariable = 1 - 1; // Assigns a value of 0
$testvariable = 2 * 2; // Assigns a value of 4
$testvariable = 2 / 2; // Assigns a value of 1
From the above examples, you can probably tell that + is the addition operator, - is the subtraction operator, * is the multiplication operator, and / is
the division operator. These are all called arithmetic operators, because they perform arithmetic on numbers.
Each of the lines above ends with a comment. Comments are a way to describe what your code is doing. They insert explanatory text into your code—text
that the PHP interpreter will ignore. Comments begin with // and they finish at the end of the same line. If you need a comment to span several lines,
you can instead start your comment with /*, and end it with */. The PHP interpreter will ignore everything between these two delimiters. I’ll use
comments throughout the rest of this book to help explain some of the code I present.
Returning to the operators, there’s another one that sticks strings of text together, called the string concatenation operator:
$testvariable = 'Hi ' . 'there!'; // Assigns a value of 'Hi there!'
Variables may be used almost anywhere that you use a literal value. Consider this series of statements:
$var1 = 'PHP'; // Assigns a value of 'PHP' to $var1
$var2 = 5; // Assigns a value of 5 to $var2
$var3 = $var2 + 1; // Assigns a value of 6 to $var3
$var2 = $var1; // Assigns a value of 'PHP' to $var2
echo $var1; // Outputs 'PHP'
echo $var2; // Outputs 'PHP'
echo $var3; // Outputs '6'
echo $var1 . ' rules!'; // Outputs 'PHP rules!'
echo "$var1 rules!"; // Outputs 'PHP rules!'
echo '$var1 rules!'; // Outputs '$var1 rules!'
Notice the last two lines in particular. You can include the name of a variable right inside a text string, and have the value inserted in its place if you
surround the string with double quotes instead of single quotes. This process of converting variable names to their values is known as variable
interpolation. However, as the last line demonstrates, a string surrounded with single quotes will not interpolate the variable names it contains.
PHP Variables, Operators, and Comments
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