Page 79 - The Unofficial Guide to Lego Mindstorms Robots

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readable names for things that might otherwise be cryptic. It also lets you define things that might need to be adjusted
th roughout your program in one place. Your program, for example, might have multiple places where it set the outputs to
power level 5. Instead of explicitly putting 5 all the way through your program, you can use the constant value POWER. If you
la ter decide you want the power level to be 7, you just have to change the definition of POWER, instead of finding all the places
he t output power i
in your program w re he s set.

You can also create macros with #define. A macro is a kind of miniature program. Usually you'll define a macro for
so mething you want to do frequently. The following program uses three macros:

#define forward(power) \
SetPower(OU T_A + OUT_C, power); \
OnFwd(OUT_A + OUT_C);
#define left(power) \
SetPower(OUT_A + OUT_C, power); \
OnRev(OUT_A); OnFwd(OUT_C);
#define right(power) \
SetPower(OUT_A + OUT_C, power); \
OnFwd(OUT_A); OnRev(OUT_C);

task main() {
forward(OUT_FULL);
Wait(100);
left(OUT_HALF);
Wait(100);
right(OUT_HALF);
Wait(100);
Off(OUT_A + OUT_C);
}

The preceding example shows off two features of macros. First, each macro has a parameter, power, that is used in the bod y
of the macro. Second, the macros are split out to multiple lines by using a backslash.

Sounds and Music

Your RCX can play various prepacka ged sounds, using the following command:

PlaySou nd(const n)
This command plays the so und represented by n. NQC includes constant names for each available sounds, as detailed in Table
4-5.

Table 4-5. RCX System Sounds

Sound Name Description

SOUND_CLICK Short beep

SOUND_DOUBLE_BEEP Two medium beeps

(table continued on next page)