How to make an arduino serial loop (receive numbers continuously) - c++

Question

New to coding! I am trying to get text on my LED Matrix through serial data that is being sent in from processing.
My code works but the only problem is that though the serial data on processing is constant, the arduino code only reads the number once. This makes it so that the text will not scroll all the way through. How do I loop a serial read on arduino?
Here is the relevant portion of my code:
void loop()
{
if (Serial.available() > 0)
{
int matrixPinState = Serial.read();
// stage = Serial.read();
// analogWrite(matrixPin, stage);
if (matrixPinState == 1)
{
matrix.fillScreen(0);
matrix.setCursor(x, 0);
matrix.print(F("Im kind"));
if (--x < -30)
{
x = matrix.width();
if (++pass >= 8) pass = 0;
matrix.setTextColor(colors[pass]);
}
matrix.show();
delay(30);
}
}
}

Answer 1

When a byte(or you call it character, a data that is 8 bit long) is fetched by uart block(the hardware), it is buffered to input buffer so that programmer can read and process it.
In your case, when you send a character, it is fetched and put to the buffer and when you read it there is no more byte available to read unless you send to new one.
In short, read the pin state once. You can do something like:
int matrixPinState = 0
void setup() {
// do all your setup settings first
while (Serial.available() < 0) {
// wait here for the input
delay(30);
}
// got your input, read it
matrixPinState = Serial.read();
}
void loop()
{
if (matrixPinState == 1)
{
matrix.fillScreen(0);
matrix.setCursor(x, 0);
matrix.print(F("Im kind"));
if (--x < -30)
{
x = matrix.width();
if (++pass >= 8) pass = 0;
matrix.setTextColor(colors[pass]);
}
matrix.show();
delay(30);
}
}