Page 87 - The Unofficial Guide to Lego Mindstorms Robots

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Table 4-7. Argument Passing for Inlines

Type By Value or By Reference? Temporary Variable Used?

i nt by value yes

c onst int by value no

int& by reference no

co nst int& by re ference no

If you pass int by value, the parameter's value is copied into a temporary variable (from the pool of 31) and used in the
inline. const int passes by value, but the value must be a constant at compile time.

If you pass by reference, the variable that is passed in can actually be modified in the inline. In this code, for example, a
count variable is incremented in the body of an inline:

task main() {
int count = 0;
while (count <= 5) {
PlaySound(SOUND_CLI CK);
Wait(count ∗ 20);
increment(count);
}
}
void increment(int& n) {
n++;
}

Th e last option, const int &, is u sed when you want to pass a value that should not be changed. This is great for things
like Sensor() and Timer(). For e xample, you might have an inline like this:

void forward(const int& power) {
SetPower(OUT_A + OUT_C, power);
OnFwd(OUT_A + OUT_C);
}

With this inline, you can do normal things, like passing a variable or constant:

int power = 6;
for war d(power);

forward(OUT_HALF);

But you can also do trickier stuff, like this:

forward(Message());

You can basically accomplish the same stuff with int parameters and const int& parameters. The advantage of const
int& is that no temporary variables are used.