﻿ Modifying the for Loop Javascript validator     Website design ﻿

## Modifying the for Loop

Once you understand the basics of the for loop structure, you can modify it in a couple of interesting ways. You can build a loop that counts by fives, or one that counts backwards.

### Counting by Fives

The countByFive.php program shown in Figure 4.4 illustrates a program that counts by fives. Figure 4.4: This program uses a for loop to count by five.

The program is very much like the basicArray program, but with a couple of twists.

```<html>

<title>
Counting By Fives
</title>

<body>

<h1>Counting By Fives</h1>

<?

for (\$i = 5; \$i <= 50; \$i+= 5){
print "\$i <br>\n";
} // end for loop

?>

</body>
</html>
```

The only thing I changed was the various parameters in the for statement. Since it seems silly to start counting at 0, I set the initial value of \$i to 5. I decided to stop when \$i reached 50 (after ten iterations). Each time through the loop, \$i will be incremented by 5. The += syntax is used to increment a variable.

```\$i += 5;
```

is exactly like

```\$i = \$i + 5;
```

### Counting Backwards

It is fairly simple to modify a for loop so it counts backwards. Figure 4.5 illustrates this feat. Figure 4.5: This program counts backwards from ten to one using a for loop.

Once again, the basic structure is just like the basic for loop program, but by changing the parameters of the for structure I was able to alter the behavior of the program. The code for this program shows how it is done.

```<html>

<title>
Counting Backwards
</title>

<body>

<h1>Counting Backwards</h1>

<?

for (\$i = 10; \$i > 0; \$i--){
print "\$i <br>\n";
} // end for loop

?>

</body>
</html>
```

If you understand how for loops work, the changes will all make sense. I'm counting backwards this time, so \$i begins with a large value (in this case 10.) The condition for continuing the loop is now \$i > 0, which means the loop will continue as long as \$i is greater than zero. As soon as \$i is zero or less, the loop will end. Note that rather than adding a value to \$i, this time I decrement by one each time through the loop. If you're counting backwards, you must be very careful that the sentry variable has a mechanism for getting smaller, or the loop will never end. Recall that \$i++ adds one to \$i. \$i- - subtracts one from \$i. Javascript validator     Website design

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