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Unit 5: Strings

5.2.1 echo Notes
To put a string into the HTML of a PHP-generated page, use echo. While it looks and for the
most part behaves like a function, echo is a language construct. This means that you can omit the
parentheses, so the following are equivalent:
echo “Printy”; echo(“Printy”); // also valid
You can specify multiple items to print by separating them with commas:
echo “One”, “Two”, “three”; OneTwothree
It is a parse error to use parentheses when trying to echo multiple values:
// this is a parse error echo (“Hello”, “world”);
Because echo is not a true function, you cannot use it as part of a larger expression:
// parse error if (echo (“test”)) {echo (“it worked!”) ;}
Such errors are easily remedied, though, by using the print ( ) or printf( ) functions.
5.2.2 print ( )
The print ( ) function sends one value (its argument) to the browser. It returns true if the string
was successfully displayed and false otherwise (e.g. if the user pressed the Stop button on browser
before this part of the page was rendered):
if (! print(“Hello, Dear”)) { die(“you are not listening to me!”); } Hello, Dear.
5.2.3 printf( )

The printf( ) function outputs a string built by substituting values into a template (the format string).
It is derived from the function of the same name in the standard C library. The first argument to
printf( ) is the format string. The remaining arguments are the values to be substituted in.
A %character in the format string indicates a substitution.

Format Modifiers
Each substitution marker in the template consists of a percent sign (%), possibly followed by
modifiers from the following list, and ends with a type specifier. (Use ‘%%’ to get a single percent
character in the output.) The modifiers must appear in the order in which they are listed here:

• A padding specifier denoting the character to use to pad the results to the appropriate string
size. Specify 0, a space, or any character prefixed with a single quote. Padding with spaces
is the default.
• A sign. This has a different effect on strings than on numbers. For strings, a minus (–) here
forces the string to be right-justified (the default is to left-justify). For numbers, a plus (+)
here forces positive numbers to be printed with a leading plus sign (e.g. 35 will be printed
as +35).
• The minimum number of characters that this element should contain. If the result is less
than this number of characters, the sign and padding specifier govern how to pad to this
length.
• For floating-point numbers, a precision specifier consisting of a period and a number;
this dictates how many decimal digits will be displayed. For types other than double, this
specifier is ignored.

Type Specifiers
The type specifier tells printf( ) what type of data is being substituted. This determines the
interpretation of the previously listed modifiers. There are eight types, as listed in Table 5.2.

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