Serial monitor problem

Projects Programming
1

Hi!

I just made a code that is supposed to calculate a circumference of a circle.

void setup()
{
	Serial.begin(9600);
}
int incomingByte = 0;

void loop()
	char buffer[100];{

    if (Serial.available() > 0) {
    	int circle(int incomingByte);
    	float Pi = 3.141592;
    	int incomingByte = Serial.readBytes(buffer, 9);
        atof(incomingByte);
    	Serial.println("");
    	Serial.println(Pi*2*incomingByte);
    }
}

When i send number 1 to COM, the result is 6.28.
When i send number 2 to COM, the result is also 6.28.

The same happens with numbers 1.1 and 2.2.

Why are the calculations always the same???

2

your code doesn't compile... and there are too many things wrong to comment exhaustively until you get that right.

but a few pointers:

Serial.readBytes() returns the number of characters placed in the buffer. A 0 means no valid data was found.

so as long as you enter one byte, you will get the same result here:

atof(incomingByte);

it seems like you are expecting more, trying get nine bytes...

Serial.readBytes(buffer, 9);
3

Read this: Serial.readBytes() - Arduino Reference

I think you want Serial.parseFloat();

Your sketch won't compile for me:

sketch_oct18b:8: error: expected initializer before 'char'
 char buffer[100]; {
 ^
sketch_oct18b:8: error: expected unqualified-id before '{' token
 char buffer[100]; {
                   ^
exit status 1
expected initializer before 'char'

That bracket is in the wrong place. Fixing that mistake gets me this warning:

/Users/john/Documents/Arduino/sketch_oct18b/sketch_oct18b.ino: In function 'void loop()':
/Users/john/Documents/Arduino/sketch_oct18b/sketch_oct18b.ino:14:22: warning: invalid conversion from 'int' to 'const char*' [-fpermissive]
     atof(incomingByte);
                      ^
In file included from /Users/john/Library/Arduino15/packages/arduino/hardware/avr/1.6.19/cores/arduino/Arduino.h:23:0,
                 from sketch/sketch_oct18b.ino.cpp:1:
/Users/john/Library/Arduino15/packages/arduino/tools/avr-gcc/4.9.2-atmel3.5.4-arduino2/avr/include/stdlib.h:361:15: note: initializing argument 1 of 'double atof(const char*)'
 extern double atof(const char *__nptr);
               ^
Sketch uses 4202 bytes (13%) of program storage space. Maximum is 32256 bytes.
Global variables use 202 bytes (9%) of dynamic memory, leaving 1846 bytes for local variables. Maximum is 2048 bytes.

I'm kind of surprised that " int circle(int incomingByte);" parses at all. It looks like a function prototype inside loop()!

I think what you meant to do is:

const float Pi = 3.141592;

void setup() {
  Serial.begin(9600);
}

void loop() {
  float inputValue = Serial.parseFloat();
  Serial.println();
  Serial.println(Pi * 2 * inputValue);
}
4

johnwasser:
I'm kind of surprised that " int circle(int incomingByte);" parses at all. It looks like a function prototype inside loop()!

that is a valid int constructor, even though it is being initialized with an un-initialized value...

void setup()
{
  Serial.begin(9600);
  int myValue(5);
  Serial.println(myValue);
}

void loop()
{

}
5

Thank you, johnwasser and BulldogLowell!

My code now works and everyhing is fine.

Both will get +1 karma.

Thank you!

6

And the sketch compiled normally for me without any warnings.
That's weird