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for loop - how it works (Perl, PHP, Java, C, etc)
When writing a program, you'll often want to repeat a block of code, counting up through a table or performing a block of code with an input value (loop counter) that goes up 1, 2, 3, 4 etc.
You COULD do this using a while loop, but this means you have to specify each of • how to start (initialise) the loop counter • how to test the loop counter to see if it's completed • how to alter the loop counter each time round and to do each of these separately means that the maintainer of the code is going to have to look in three places at once to work out what's going on. Most languages have a for loop construct which pulls all three elements into one statement, for example: for ($k=0; $k<25; $k++) { which means START at zero, REPEAT the loop while $k is less that 25 and before EACH SUBSEQUENT test and loop add 1 to $k. Here's a diagram to show how that works ![]() The GREEN shows the initial entry to the loop, where the initial value is set and then the condition is tested. The ORANGE shows each subsequent time round the loop, where the last clause (the increment) is performed before the condition is retested and the RED shows how the loop exits once the condition has gone false. You'll note that a for loop CAN exit straight away, since the test is done on entry as well as each time the last clause has been run. (written 2007-06-06 10:02:57) Associated topics are indexed under H104 - PHP - Control StatementsY104 - Python - Lists and Tuples P206 - Perl - More Loops and Conditionals C203 - C and C based languages - Conditionals and Loops R104 - Ruby - Control Structures J704 - Java - Loops and Conditional Statements
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Object Relation Mapping (ORM)Asda opening large new store in Melksham Perl, the substitute operator s Bathtubs and pecking birds for loop - how it works (Perl, PHP, Java, C, etc) Judging the quality of contributed Perl code Sunday afternoon What are factory and singleton classes? Five of the best - pictures from London An update on Perl - where is it going? 1690 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 at 50 posts per pageThis is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price. Link to Ezine home page (for reading). Link to Blogging home page (to add comments). |
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