How to write this -> n (n + 1) / 2 <- expression without errors in objective - C

Can you show preciselywhat you want to achieve with the code and the error, not just in the title of the thread.

What do you mean with <- operator ?

n (n + 1) / 2 is a formula, but for some reason when i put that into xcode, i get an error message, even when i replace the n with numbers i still get errors. Here is the actual problem:

A triangular number can also be generated by the formula:

triangularNumber = n (n + 1) / 2

for any integer value of n. For example, the 10th triangular number number, 55, can be generated by substituting 10 as the value for n in the preceding formula.

......ps the -->> is just to point out the formula.