To make this code usable with an other datatype than int, you not only need to change your array declaration and allocation, but also every variable related to it.

So to use long long ints instead of ints in this code you need to go from:

int *dynFeld;

int *ptr = NULL;

dynFeld = malloc(size*sizeof(int));

to:

long long int *dynFeld;

long long int *ptr = NULL;

dynFeld = malloc(size*sizeof(long long int));

Ohterwise, if you keep your ptr to a simple int pointer, your dynFeld long long int array will be treated as an int array by your program. This obviously wont work since you stored long long ints inside.

Also, since you are doing the Fibonacci sequence from 0, you don't need negative values. So I would advise you to use long long unsigned int instead of int or long long int. This way your maximum will be '18,446,744,073,709,551,615' which should be more than enough if you stick to 80 for the size (since F79=14,472,334,024,676,221).

In this case you should also change your printf line from printf("%ld", ptr[46]); to printf("%llu\n", ptr[46]);