/* An implementation of the fast-growing "M" function */

#include <stdio.h>

/*
An implementation of the hyperoperation sequence (analogous to S0(n)).
*/
int hyp(int n, int a, int b) {
    if(n == 0) {return b+1;}
    else if(n == 1 && b == 0) {return a;}
    else if(n == 2 && b == 0) {return 0;}
    else if(n >= 3 && b == 0) {return 1;}
    else {return hyp(n-1,a,hyp(n,a,b-1));}
}

/*
An implementation of the "S" function, with an array input
*/
int S(int inputArr[], int n) {
    int size = sizeof(inputArr)/sizeof(inputArr[0]);
    if(size == 1) {
        if(inputArr[0] == 0) {return hyp(n,n,n);}
        else {
            int counter = 1;
            int passArray[]={inputArr[0]-1};
            int k = S(passArray,n);
            while(counter < n) {
                k = S(passArray,k);
                counter = counter+1;
            }
            return k;
        }
    }
    else if(inputArr[size-1] == 0) {
        int newArray[size-1];
        int f;
        for(f = 0; f < size-1; f++) {
            newArray[f] = inputArr[f];
        }
        return S(newArray,n);
    }
    else {
        int newArray[size];
        int midArray[size];
        int f;
        for(f = 0; f < size-2; f++) {
            newArray[f] = inputArr[f];
        }
        for(f = 0; f < size-1; f++) {
            midArray[f] = inputArr[f];
        }
        midArray[size-1] = inputArr[size-1]-1;
        newArray[size-1] = inputArr[size-1]-1;
        newArray[size-2] = S(midArray,n);
        return S(newArray,n);
    }
}

/*
The "M" function, based on the "S" function defined above
*/
int M(int n) {
    int callArray[n];
    int k;
    for(k = 0; k < n; k++) {callArray[k] = n;}
    return S(callArray,n);
}

int main() {
    int n = 0;
    int k = M(n);
    printf("M(%d) = %dn",n,k);
    n = 1;
    k = M(n);
    printf("M(%d) = ",n);
    printf("%dn",k);
    n = 2;
    printf("M(%d) = ",n);
    k = M(n);
    printf("%dn",k);
return 0; }