View source for Subn

The '''subn''' command subtracts a numerical value from a variable.

== Syntax ==

subn([[variable|var]] vA, [[number|byt]] B);<br />
vA = vA - B;<br />
vA -= B;<br />

== Remarks ==

Because [[variable]]s are 8 bit unsigned numbers, if the result of the subtraction is less than 0, the result 'wraps around'. For example, if v50 currently equals
20, the statement:

<CODE>subn(v50, 25);</code>

will result in a value for v50 of 251 (20 - 25 = -5; -5 + 256 = 251).

If the value of '''B''' is 1, WinAGI will use the '''[[decrement]]''' command instead of '''subn''' if you use the alternate syntax (i.e. '''vA''' = '''vA''' - 1 or '''vA''' -= 1). To force the compiler to use '''subn''', use the full form: subn('''vA''', 1). This important because the '''decrement''' command does not wrap around like the '''subn''' command.

== Possible Errors ==

None.

== Example ==

<div class="CodeBlockHeader">Code:</div>
<syntaxhighlight lang="agi">
v50 = 40;
subn(v50, 25);  [ v50 now equals 15
v50 = v50 - 25; [ v50 now equals 246 (-10 + 256)
v50 -= 25;      [ v50 now equals 221
</syntaxhighlight>

== Technical Information ==

{| border="1" cellpadding="2"
| style="background-color: #efefef" width="200" | '''Required Interpreter Version:'''
| width="175" | Available in all AGI versions.
|-
| style="background-color: #efefef" | '''Byte-Code Value:'''
| 7 (0x07 hex)
|}

== See Also ==

[[Mathematical Commands]]<br />
'''[[subv]]'''<br />
'''[[decrement]]'''<br />
[[Category:Commands]]<br />