Ackermans function using Recursion

Recursion: Ackerman's Function

Write a program for Ackerman's function using Recursion

Ack(3,0) = ack(2,1)

                = ack(1, ack(2,0))

                = ack(1, ack(1,1))

                = ack(1, ack(0, ack(1,0)))

                = ack(1, ack(0, ack(0, 1)))

                = ack(1, ack(0, 2))

                = ack(1, 3)

                = ack(0, ack(1, 2))

                = ack(0, ack(0, ack(1, 1)))

                = ack(0, ack(0, ack(0, ack(1, 0))))

                = ack(0, ack(0, ack(0, ack(0, 1))))

                = ack(0, ack(0, ack(0, 2)))

                = ack(0, ack(0, 3))

                = ack(0, 4)

                = 5

#include<stdio.h>

double acker(int m, int n);

void main()

{

                int m, n;

                double a;

                printf("\nEnter the value of m and n:");

                scanf("%d %d", &m, &n);

                if(m<0 || n<0)

                                printf("\nEnter nonnegatives only");

                a = acker(m, n);

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

}

double acker(int m, int n)

{

                if( m == 0 )

                                return n+1;

                else if(n == 0)

                                return  acker((m-1), 1);

                else

                                return  acker( (m-1), acker(m, n-1) );

}

Output:

Enter the value of m and n:         3              0

A(3 , 0) = 5.000000