This is a simple drop-in function that will return the next number in the Fibonacci sequence every time you call it. specialcase is used to properly generate the first two numbers, 0 and 1, before dropping into the well known next = current + previous pattern. num1 and num2 are the previous and current numbers in the sequence, and since they're "static," their values will be retained between calls.
Note that return specialcase++; returns the value of specialcase before incrementing it, otherwise it would return 1, 2 instead of the needed 0, 1.
int genfib() {
static int num1=0, num2=1, specialcase = 0;
if (specialcase < 2) {
return specialcase++;
}
int num3 = num1 + num2;
num1 = num2;
num2 = num3;
return num3;
}
while (1) {
printf("%d\n", genfib());
}
The expected output is:
0
1
1
2
3
5
8
--- etc ---
There is no method to reset fibgen if you need to start over, but encapsulating the variables num1, num2, and specialcase in a struct would be trivial. Then pass the pointer to this struct to fibgen every time you call it.
int fibgen() could be easily rewritten to use 64 bit variables if a longer sequence is needed for some reason. Just change the function declaration, num1, num2, and num3 to uint64_t.