7.7 Conditional statements

Stan supports full conditional statements using the same if-then-else syntax as C++. The general format is

if (condition1)
else if (condition2)
// ...
else if (conditionN-1)

There must be a single leading if clause, which may be followed by any number of else if clauses, all of which may be optionally followed by an else clause. Each condition must be an integer value, with non-zero values interpreted as true and the zero value as false.

The entire sequence of if-then-else clauses forms a single conditional statement for evaluation. The conditions are evaluated in order until one of the conditions evaluates to a non-zero value, at which point its corresponding statement is executed and the conditional statement finishes execution. If none of the conditions evaluate to a non-zero value and there is a final else clause, its statement is executed.