wrong argument type to unary minus

Projects Programming
1

I have a problem with a my code that results in a "Wrong argument type to unary minus" message when I compile.

I am trying to get a stepper motor to turn the other way in this line. I copied the code from an official example that compiled and worked for me without a problem.

The project is experimenting with using potentiometers to change how far a stepper rotates and the speed of rotation.

I am new to coding, I've tried reviewing the help files, google etc. I have changed the variable type form floating to integer, and also tried using a couple of other approaches to get the step value to go negative (I discovered a couple of new errors with that approach)

The code is below. The problem line is at the end:

myStepper.step(-steps);

Thanks for your help,

// the setup routine runs once when you press reset:

// Stepper - Version: Latest
#include <Stepper.h>

/* Example sketch to control a 28BYJ-48 stepper motor with ULN2003 driver board and Arduino UNO. More info: https://www.makerguides.com */
// Modify to control speed and no. revolutions with potentiometers
// Include the Arduino Stepper.h library:
// Define number of steps per rotation:
const int stepsPerRevolution = 2048;
// Wiring:
// Pin 8 to IN1 on the ULN2003 driver
// Pin 9 to IN2 on the ULN2003 driver
// Pin 10 to IN3 on the ULN2003 driver
// Pin 11 to IN4 on the ULN2003 driver
// Create stepper object called 'myStepper', note the pin order:
Stepper myStepper = Stepper(stepsPerRevolution, 8, 10, 9, 11);
int steps();
int RPM();
int reverse(-1);

void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
}

void loop() {
{
// read the input on analog pin 0:
int sensorValue = analogRead(A0);
// Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
float voltage = sensorValue * (5.0 / 1023.0);
// print out the value you read:
Serial.println(voltage);
}

{
// read the input on analog pin 0:
int sensorValue = analogRead(A0);
// Convert the analog reading (which goes from 0 - 1023) to RPM (0 - 20 RPM):
float RPM = sensorValue * (20.0 / 1023.0);
// print out the value you read for troubleshooting:
Serial.println(RPM);
Serial.println("RPM");
delay(10);
// Set the speed to equal rpm:
myStepper.setSpeed(RPM);
}

{
{
// read the input on analog pin 0:
int sensorValue = analogRead(A1);
// Convert the analog reading (which goes from 0 - 1023) to steps (0 - 20 RPM):
int steps= sensorValue * (stepsPerRevolution / 1023.0);
// print out the value you read for troubleshooting:
Serial.println(steps);
Serial.println("Steps");
delay(10);
}

// Step one revolution in one direction:
Serial.println("clockwise");
myStepper.step(steps);
delay(500);

// Step one revolution in the other direction:
Serial.println("counterclockwise");
myStepper.step(-steps);
delay(500);
}
}

2 
int steps();
int RPM();
int reverse(-1);

That is not how to declare and initialize variables.

int steps;
int RPM;  // same variable name declared as float in sketch (float RPM = sensorValue * (20.0 / 1023.0))
int reverse = -1;  //  not used in sketch

Please read the how to use this forum sticky to see how to post code in code tags. Please post the entire text of any error messages. Paraphrasing leaves out important information.

3

You clearly don't know C++ - there's nothing wrong with the declaration of reverse, but the RPM and steps
lines are function prototypes. Presumably this was intended:

int steps(0);
int RPM(0);
int reverse(-1);

or

int steps;
int RPM;
int reverse(-1);