What does return (-1) in start mean?

Trading Systems Expert Advisors and Automated Trading
1

Hi everyone I am new here. I have a question about the code below. As you can see x=Period(). The if statement checks if x>240 and if true then it returns -1. What I want to know is what does returning -1 in the start() function do? what is it telling the system if its returning -1? because I know normally its returns(0) and not return(-1).
int start(){
x=Period();
if (x>240) return(-1);

  //MORE CODES BELOW

}

and also if their is MORE CODES BELOW the return(-1) will those codes execute?

2

The return of -1 means that the chart’s TF is less than 240 minutes. For some reason the coder doesn’t want to process ticks on these TF.

Once condition is met, no more execution occurs.

3

thanks. I got another question. As you can see below their is + in front of tp1 and re1. Why on earth is their a + in front of tp1 and re1? is it necessary?
MathRound((+tp1-fb)*10000)/10000;
MathRound((+re1/ri)*10)/10;