In Javascript declarations, what does "?" along with ":" mean? [duplicate]

Question

This question already has answers here:

Question mark and colon in JavaScript (8 answers)

How do you use the ? : (conditional) operator in JavaScript? (19 answers)

Closed 8 years ago.

In a Javascript program to convert a Julian day to a calendar day, the following code is seen:

 month = (G<13.5) ? (G-1) : (G-13)
  year = (month<2.5) ? (C-4715) : (C-4716)

I thought these may have been some sort of conditions that changed the values of month or year according to the values of the variables within their declarations My research has returned nothing on these symbols--particularly the "?"--showing up in Javascript code.

For a complete view of the source, visit astronomy.villanova.edu/links/jd.htm

Any help would be greatly appreciated!

Answer 1

This is called the ternary or conditional operators in javascript

It is a short hand for something like:

if(a ==0){
   b = 1;
}
else{
   b = 0;
}

Answer 2

variable = if condition is true ? give this answer : otherwise give this one;

so int x = 5; int y = x==5? 10 :12; would mean if x is equal to 5, y would be 10 , otherwise it would be 12