fib1.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

static unsigned int fib(int param)
{
    assert(param > 0);

    int f1, f2, f3 = 0;
    int i;
    for (i = 1; i <= param; i++) {
        if (i == 1 || i == 2) {
            f1 = 0;
            f2 = 1;
        }
        f3 = f2 + f1;
        f1 = f2;
        f2 = f3;
    }
    return f3;
}

int main(int argc, char *argv[]) {
    //  No Error Processing
    printf("%u", fib(atoi(argv[1])));
}