C++ Type Problem

[matmatmat]

I am developing with the Arduino & it's C++ like language. I am trying to create something like a metronome everytime a button is pressed this functions is called:


//function
void setSpeed(int i){
spd = i;

odel = spd;
odel = odel * 1000;
odel = (float) odel / spd;

del = odel;
del = del / 100;
del = del * 90;

del2 = odel;
del2 = del2 / 100;
del2 = del2 * 10;

Serial.println(del); //Print del out
}

//--snip--//
//call

//if the button is pressed:
setSpeed(spd + 1);

when I call the function it outputs the same number each time, 900. I think this is something to do with the division:


odel = (float) odel / spd;

[MadCow108]

your code is missing all types, its that a feature of Arduino?

if the missing types are not the problem then I guess this is:
setSpeed(spd + 1);
this (in normal C++) creates a temporary with spd + 1 and passes that to the function but does not alter spd
you probably want this:
setSpeed(++spd);

this first increases speed and passes the increased spd to the function. (contrary to spd++ which first passes the unaltered spd to the function and then increases it)

[matmatmat]

Sorry forgot to post them, full listing:


int pin = 9;
int switchPin = 2;

int buttonState;

int val, val2;

int interval = 0;
int value = LOW;

long previousMillis = 0;

int spd;
long odel;
float del;
float del2;

void setSpeed(int i){
spd = i;

odel = spd;
odel = odel * 1000;
odel = (float) odel / spd;

del = odel;
del = del / 100;
del = del * 90;

del2 = odel;
del2 = del2 / 100;
del2 = del2 * 10;

Serial.println(del);
}

void setup(){
pinMode(pin, OUTPUT);
Serial.begin(9600);

setSpeed(60);

buttonState = digitalRead(switchPin);
}

void loop(){
val = digitalRead(switchPin);
delay(10);
val2 = digitalRead(switchPin);
if (val == val2) {
if (val != buttonState) {
if (val == LOW) {
setSpeed(++spd);
}
}
buttonState = val;
}

if(millis() - previousMillis > interval){
if (value == LOW) {
value = HIGH;
interval = del2;
} else {
value = LOW;
interval = del;
}
//Serial.print(interval);
//Serial.print("\n");
previousMillis = millis();
digitalWrite(pin, value);
}
}

[MadCow108]

just saw the problem:
odel = spd;
odel = odel * 1000;
odel = (float) odel / spd;

lets rewrite that:
odel = (spd * 1000) / spd = (spd/spd) * 1000 = 1 * 1000
result: always 1000 because its independent of spd

so you always get 900 as output

[matmatmat]

Thanks, that sould of calculated the number of seconds per beat (eg 1s for 60bpm) -- to do that is it:


//replace
odel = (float) odel / spd;

//with
odel = odel/60;