Ackermann Function

Ackermann Function is the simplest example of a well defined total function which is compatible but not primitive recursive. It grows faster than an exponential function.

/* Ackermann Function */
#include<stdio.h>
#include<stdlib.h>

int count = 0, indent = 0;

int ackermann(int x, int y)
{
	count++;
	if(x<0 || y<0) return -1;
	if(x==0)  return y+1;
	if(y==0) return ackermann(x-1,1);
	return ackermann(x-1,ackermann(x,y-1));
}


int main()
{
	int x,y;
        printf("Enter values for x and y : ");
        scanf("%d%d",&x,&y);
        printf("Result is %d\n",ackermann(x,y));
	printf("\nFunction called %d times.\n",count);
}