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Writing Joystick Code: Part 3: Difference between revisions
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We write then as {, and endif as }. | We write then as {, and endif as }. | ||
And each "action" is terminated by a semicolon: | |||
Lets say that if x is less than 5 we want to add 2 to it. We write | |||
if (x < 5) { x = x + 2 } | |||
Lets say that if x is less than 5 we want to add 2 to it. We write: | |||
<syntaxhighlight lang="php"> | |||
if (x < 5) { x = x + 2; } | |||
</syntaxhighlight> | |||
The more readable way of writing it is | The more readable way of writing it is | ||
<syntaxhighlight lang="php"> | |||
if (x < 5) { | if (x < 5) { | ||
x = x + 2 | x = x + 2; | ||
} | } | ||
</syntaxhighlight> | |||
If we also want to add 1 to y if the condition is true, we write | If we also want to add 1 to y if the condition is true, we write | ||
<syntaxhighlight lang="php"> | |||
if (x < 5) { | if (x < 5) { | ||
x = x + 2; | x = x + 2; | ||
y + y + 1 | y + y + 1; | ||
} | } | ||
</syntaxhighlight> | |||
Now lets pretend that we still want to increase x by 2 if it less than 5, and if it is 5 or more we want to add 1 to it. We use else. | Now lets pretend that we still want to increase x by 2 if it less than 5, and if it is 5 or more we want to add 1 to it. We use else. | ||
It looks like this | It looks like this | ||
<syntaxhighlight lang="php"> | |||
if (x < 5) { | if (x < 5) { | ||
x = x + 2 | x = x + 2; | ||
} | } | ||
else { | else { | ||
x = x + 1 | x = x + 1; | ||
} | } | ||
</syntaxhighlight> | |||
Now lets say we have the following rules: | Now lets say we have the following rules: | ||
| Line 121: | Line 132: | ||
Writing our code properly we get | Writing our code properly we get | ||
<syntaxhighlight lang="php"> | |||
if (x < 5) { | if (x < 5) { | ||
x = x + 2 | x = x + 2; | ||
} | } | ||
elseif (x < 10) { | elseif (x < 10) { | ||
x = x + 1 | x = x + 1; | ||
} | } | ||
else { | else { | ||
x = x + 7 | x = x + 7; | ||
} | } | ||
</syntaxhighlight> | |||
You can use more than one elseif, but it gets messy. If you have a number of tests then it is better to test for each case individually. | You can use more than one elseif, but it gets messy. If you have a number of tests then it is better to test for each case individually. | ||
Easier to understand and much less chance of an error. | Easier to understand and much less chance of an error. | ||
Our above example would become | Our above example would become | ||
<syntaxhighlight lang="php"> | |||
if (x < 5) { | if (x < 5) { | ||
x = x + 2 | x = x + 2; | ||
} | } | ||
if (x >= 5) and (x < 10) { | if (x >= 5) and (x < 10) { | ||
x = x + 1 | x = x + 1; | ||
} | } | ||
if (x >= 10) { | if (x >= 10) { | ||
x = x + 7 | x = x + 7; | ||
} | } | ||
</syntaxhighlight> | |||
Because each if is tested we need to have the (x >= 5) otherwise if x = 1 both the first and second if conditions would be satisfied. | Because each if is tested we need to have the (x >= 5) otherwise if x = 1 both the first and second if conditions would be satisfied. | ||
| Line 150: | Line 166: | ||
Lets say that you want something to happen only if the gear is up. But the only property you can read is Gear-Down. Then you write | Lets say that you want something to happen only if the gear is up. But the only property you can read is Gear-Down. Then you write | ||
<syntaxhighlight lang="php"> | |||
if (!Gear-Down) { | if (!Gear-Down) { | ||
action | action; | ||
} | } | ||
</syntaxhighlight> | |||
The ! means not. So it translates as: If the gear is not down perform action. | The ! means not. So it translates as: If the gear is not down perform action. | ||
Beacuse we use < and > we will need to enclose it all with CDATA. | Beacuse we use < and > we will need to enclose it all with CDATA, in order not to mess up the XML syntax. | ||
See the discussion of variables below for an example of the use of if. | See the discussion of variables below for an example of the use of if. | ||