Fibonacci numbers

/*  A command-line program to compute (huge) Fibonacci numbers. An old program,
    not very efficient concerning memory usage. To compile run: cc -ansi -o fib fib.c
    Copyright (C) <September 1, 1992> Henning POLZER, h underscore polzer at gmx dot de

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

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

#define M 210   /* maximale Anzahl der Stellen; 1000. Fibonacci-Zahl hat 209 Stellen */

int             v[M], nv[M], erg[M], i, z;

void
berechne(void)
{
    for (i = M - 1; i >= 0; i--) {
        if ((erg[i] = v[i] + nv[i]) > 9) {
            erg[i] -= 10;
            v[i - 1]++;
        }
        v[i] = nv[i];
        nv[i] = erg[i];
    }
}

void
aktuell(void)
{
    int             k = 0;

    while (!erg[k])
        k++;

    for (i = k; i < M; i++)
        printf("%d", erg[i]);
}

int
main(int argc, char *argv[])    /* Ausgabe erst ab 3. Fibonacci-Zahl (= 2) */
{
    v[M - 1] = nv[M - 1] = 1;

    for (z = 1; z < atoi(argv[1]) - 1; z++)
        berechne();

    aktuell();
    printf("\n");
    return 0;
}