Pad with leading zeroes:

 
<?
    $red = 1;
    $green = 1;
    $blue = 1;
    printf( "#%02x%02x%02x", $red, $green, $blue);
?>

1.	@printf(" Maths: %d; English: %d; History: %d; Biology: %d. \n"
2.	Adding the and tags so the spaces display
3.	printf and format
4.	printf and string format
5.	printf puts the numbers into the string
6.	printf() Type Specifiers
7.	printf() and Type Specifiers
8.	printf() and sprintf() Formatting Types
9.	printf() and sprintf() Formatting Types
10.	Displaying signs with printf()
11.	Format an integer and a floating-point value with the printf() function.
12.	Format strings for use in printf( )
13.	Formatting a price with printf()
14.	The printf function formats complex strings using a single expression.
15.	Use printf to output float numbers
16.	Using printf() to Format a List of Product Prices
17.	Working with printf()
18.	Zero-padding with printf()
19.	int printf ( string format [, mixed argument [, mixed ...]] ) is the standard C way to format text
20.	Demonstrating Some Type Specifiers
21.	Displaying a real number in money format
22.	Displaying long text with an ellipsis
23.	Displaying the same number in different formats
24.	Example: Displaying a number in binary format
25.	Left-aligned by prepending a minus symbol (-) to the field width specifier
26.	When you specify a color in HTML, you combine three hexadecimal numbers between 00 and FF.
27.	Padding Output with the Padding Specifier

Pad with leading zeroes: : printf « Utility Function « PHP