Math problem "invalid conversion"

Using Arduino Programming Questions
1

Hi

I have a small probably very simple problem I cant figure out. I do some math in my if statements below, but there is some problem with it. Among others I get the following error message "warning: invalid conversion from 'long unsigned int (*)()' to 'long int' [-fpermissive]
StartMillis = millis;
"

Best regards
Rasmus

#include "MegunoLink.h" // Helpful functions for communicating with MegunoLink.
#include <Wire.h>

// Interval (milliseconds) between sending analog data
const unsigned SendInterval = 20; // [ms]
 
// The plot we are sending data to.
TimePlot MyPlot;

// constants won't change. Used here to set pin numbers:
int ControlPin = 6;      // LED connected to digital pin 9
int buttonPin =  12;      // The number of the pin controlled by the button

// Variables will change:
int val = 25;         // variable to store the value calculated based on time passed since the test was started.
long StartMillis = 0; // Millis value when test was started. 
int Flag = 0; // flag to mark if the test should be ongoing


void setup() {
  Wire.begin();
  Serial.begin(9600);
  pinMode(ControlPin, OUTPUT);  // sets the pin as output
  pinMode(buttonPin, INPUT);  // sets the pin as input
}

void loop() {
if (digitalRead(buttonPin) == LOW) {
      delay(1000);
      Serial.println( "New test initiated");
      Flag = 1;
      StartMillis = millis;
    }

if (Flag == 1) {
      val = floor(((millis - StartMillis) / 500) + 25);  // Calculate val based on time elapsed
      analogWrite(ControlPin, val); // AnalogWrite values from 0 to 255
    }  

if ((millis - StartMillis) > 60000) {
  Flag = 0;
  delay (5000);
  val = 25;
  analogWrite(ControlPin, val); // AnalogWrite values from 0 to 255
  }
}
2

Please follow the advice given in the link below when posting code. Use code tags (the </> icon above the compose window) to make it easier to read and copy for examination

3

Thanks for adding the code tags

millis() returns an unsigned long
You have StartMillis declared as a signed long

Please post the complete error messages (using code tags) copied from the IDE using the "Copy Error message" button

4 
Arduino: 1.8.13 (Windows 10), Board: "Arduino Uno"





















C:\Users\rafb\AppData\Local\Temp\untitled145637832.tmp\sketch_sep15a\sketch_sep15a.ino: In function 'void loop()':

C:\Users\rafb\AppData\Local\Temp\untitled145637832.tmp\sketch_sep15a\sketch_sep15a.ino:32:21: warning: invalid conversion from 'long unsigned int (*)()' to 'long int' [-fpermissive]

       StartMillis = millis;

                     ^~~~~~

C:\Users\rafb\AppData\Local\Temp\untitled145637832.tmp\sketch_sep15a\sketch_sep15a.ino:36:28: warning: pointer to a function used in arithmetic [-Wpointer-arith]

       val = floor(((millis - StartMillis) / 500) + 25);  // Calculate val based on time elapsed

                     ~~~~~~~^~~~~~~~~~~~~

sketch_sep15a:36:43: error: invalid operands of types 'long unsigned int (*)()' and 'int' to binary 'operator/'

       val = floor(((millis - StartMillis) / 500) + 25);  // Calculate val based on time elapsed

                    ~~~~~~~~~~~~~~~~~~~~~~~^~~~~

C:\Users\rafb\AppData\Local\Temp\untitled145637832.tmp\sketch_sep15a\sketch_sep15a.ino:40:13: warning: pointer to a function used in arithmetic [-Wpointer-arith]

 if ((millis - StartMillis) > 60000) {

      ~~~~~~~^~~~~~~~~~~~~

C:\Users\rafb\AppData\Local\Temp\untitled145637832.tmp\sketch_sep15a\sketch_sep15a.ino:40:30: warning: ISO C++ forbids comparison between pointer and integer [-fpermissive]

 if ((millis - StartMillis) > 60000) {

                              ^~~~~

exit status 1

invalid operands of types 'long unsigned int (*)()' and 'int' to binary 'operator/'



This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.
5 
if ((millis - StartMillis) > 60000)

millis is a function so this should be

if ((millis() - StartMillis) > 60000)
6

Thanks. That cleared all the errors.

I changed StartMillis to be an unsigned long also, but that may not have been necessary? Will it change automatically when I assign millis() to it?

7

You are probably OK mixing types as the compiler will promote data types but why not do it right ?

8

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