c - Iterative Fibonacci algorithm giving me a wrong result after fib(47) -

i using iterative fib algorithm have copied below. have found algorithm on rosetta code , gives me correct answer until fib(46). after values wrong. know why case?

long long fibb(int n) {     int fnow = 0, fnext = 1, tempf;     while(--n > 0) {         tempf = fnow + fnext;         fnow = fnext;         fnext = tempf;     }     return fnext;    } 

output:

fib(46) = 1836311903            <---- correct fib(47) = 18446744092385799393   <---- wrong (correct answer is: 2971215073) 

notice using temporary variables of type int in code rather type long long int. means if point you're dealing sufficiently large fibonacci numbers, you'll integer overflow in code. in particular, 47th fibonacci number 2,971,215,073, large fit in signed 32-bit integer, you'll overflow.

changing temporary variables type long long int (or, better yet, uint64_t) should fix this.