## 2.16.1. ProblemYou want to perform mathematical operations with numbers formatted not in decimal, but in octal or hexadecimal. For example, you want to calculate web-safe colors in hexadecimal. ## 2.16.2. SolutionPrefix the number with a leading symbol, so PHP knows it isn't in base 10. The following values are all equal: 0144 // base 8 100 // base 10 0x64 // base 16 Here's how to count from decimal 1 to 15 using hexadecimal notation: for ($i = 0x1; $i < 0x10; $i++) { print "$i\n"; } ## 2.16.3. DiscussionEven if you use hexadecimally formatted numbers in a for ($i = 0x1; $i < 0x10; $i++) { print dechex($i) . "\n"; } For most calculations, it's easier to use decimal. Sometimes, however, it's more logical to switch to another base'for example, when using the 216 web-safe colors. Every web color code is of the form is the red color, RR is the green color, and GG is the blue color. Each color is actually a two-digit hexadecimal number between 0 and FF.BBWhat makes web-safe colors special is that , and GG each must be one of the following six numbers: 00, 33, 66, 99, CC, or FF (in decimal: 0, 51, 102, 153, 204, or 255). So 003366 is web safe, but 112233 is not. Web-safe colors render without dithering on a 256-color display.BBWhen creating a list of these numbers, use hexadecimal notation in this triple-loop to reinforce the list's hexadecimal basis, as shown in Example 2-9. ## Printing out all the web-safe color codes
Here the loops compute all possible web-safe colors. However, instead of stepping through them in decimal, you use hexadecimal notation, because it reinforces the hexadecimal link between the numbers. Print them out using ## 2.16.4. See AlsoRecipe 2.15 for details on converting between bases; Chapter 3, "Web Design Principles for Print Designers," in Web Design in a Nutshell by Jennifer Niederst Robbins (O'Reilly) . |

PHP Cookbook: Solutions and Examples for PHP Programmers

ISBN: 0596101015

EAN: 2147483647

EAN: 2147483647

Year: 2006

Pages: 445

Pages: 445

Authors: Adam Trachtenberg, David Sklar

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