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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 a real or 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.