Ackermann function computed recursively

ackermann_recursive.c

/*
 *  Copyright (c) 2020 by Reto Kromer
 *
 *  Ackermann function:
 *
 *    A(0,n) = n+1
 *    A(m,0) = A(m-1,1)         if m > 0
 *    A(m,n) = A(m-1,A(m,n-1))  if m > 0 and n > 0
 *
 *    where m and n are non-negative integers
 *
 *  computed recursively.
 * 
 *  This C program is released under a 3-Clause BSD License and is provided
 *  "as is" without warranty or support of any kind.
 */

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


unsigned int A(unsigned int m, unsigned int n) {
  return m == 0 ? n+1 : ( n == 0 ? A(m-1,1) : A(m-1,A(m,n-1)) );
}


int main(int argc, char* argv[]) {
  unsigned int m, n;

  if (argc == 3) {
    m = atoi(argv[1]);
    n = atoi(argv[2]);
  } else {
    printf("%s", "m = ");
    scanf("%d", &m);
    printf("%s", "n = ");
    scanf("%d", &n);
  }

  printf("A(%d,%d) = %d\n", m, n, A(m,n));

  return 0;
}