Posting Data into MySQL - Invalid Operators

Hi there, I've adopted some of my old code into new code to create a data logger. I'm looking to read data from 6 sensors and post it into a table in MySQL. I've found some guides on instructables and tried to adopt my code. However I get an invalid operator on the line data= (or line 58). It's flagging up on the bit I have copied though - does anyone have any idea why?

void loop(){

	currentMillis = millis();
	if(currentMillis - previousMillis > interval) { // READ ONLY ONCE PER INTERVAL
		previousMillis = currentMillis;
    p1 = (int) readPressure1();
    p2 = (int) readPressure2();
    p3 = (int) readPressure3();
    p4 = (int) readPressure4();
    p5 = (int) readPressure5();
    p6 = (int) readPressure6();

	data = "p1=" + p1 + "&p2=" + p2 + "&p3=" + p3 + "&p4=" + p4 + "&p5=" + p5 + "&p6=" + p6;

	if (client.connect("",80)) { // REPLACE WITH YOUR SERVER ADDRESS
		client.println("POST /add.php HTTP/1.1"); 
		client.println("Host:"); // SERVER ADDRESS HERE TOO
		client.println("Content-Type: application/x-www-form-urlencoded"); 
		client.print("Content-Length: "); 

	if (client.connected()) { 
		client.stop();	// DISCONNECT FROM THE SERVER


I've attached my script if you like to see the whole picture.

client.ino (11.1 KB)

does anyone have any idea why?

Sure. The right side of the = sign is evaluated, and the result stored in the variable on the right.

Grab your calculator, and add "p1=" and the value in p1. What did you get? Post a picture of the screen.

The + is NOT a "concatenate these data elements, automatically converting ints to strings as needed" operator.

The sprintf() function CAN do that.

Actually, according to
you can use the + Operator to concatenate strings.

I would suggest, simply for test purposes, reducing line 58 to date = "p1=".

Add in Piece by Piece until you get the error. Does that give any insight?

Actually, according to
you can use the + Operator to concatenate strings.

That applies ONLY if there are Strings involved. "p1=" is a string, NOT a String.