Task: Fractran

C: #include <stdio.h>
#include <stdlib.h>
#include <gmp.h>

typedef struct frac_s *frac;
struct frac_s {
	int n, d;
	frac next;
};

frac parse(char *s)
{
	int offset = 0;
	struct frac_s h = {0}, *p = &h;

	while (2 == sscanf(s, "%d/%d%n", &h.n, &h.d, &offset)) {
		s += offset;
		p = p->next = malloc(sizeof *p);
		*p = h;
		p->next = 0;
	}

	return h.next;
}

int run(int v, char *s)
{
	frac n, p = parse(s);
	mpz_t val;
	mpz_init_set_ui(val, v);

loop:	n = p;
	if (mpz_popcount(val) == 1)
		gmp_printf("\n[2^%d = %Zd]", mpz_scan1(val, 0), val);
	else
		gmp_printf(" %Zd", val);

	for (n = p; n; n = n->next) {
		
		if (!mpz_divisible_ui_p(val, n->d)) continue;

		mpz_divexact_ui(val, val, n->d);
		mpz_mul_ui(val, val, n->n);
		goto loop;
	}

	gmp_printf("\nhalt: %Zd has no divisors\n", val);

	mpz_clear(val);
	while (p) {
		n = p->next;
		free(p);
		p = n;
	}

	return 0;
}

int main(void)
{
	run(2,	"17/91 78/85 19/51 23/38 29/33 77/29 95/23 "
		"77/19 1/17 11/13 13/11 15/14 15/2 55/1");

	return 0;
}








VB: Option Base 1
Public prime As Variant
Public nf As New Collection
Public df As New Collection
Const halt = 20
Private Sub init()
    prime = [{2,3,5,7,11,13,17,19,23,29,31}]
End Sub
Private Function factor(f As Long) As Variant
    Dim result(10) As Integer
    Dim i As Integer: i = 1
    Do While f > 1
        Do While f Mod prime(i) = 0
            f = f \ prime(i)
            result(i) = result(i) + 1
        Loop
        i = i + 1
    Loop
    factor = result
End Function
Private Function decrement(ByVal a As Variant, b As Variant) As Variant
    For i = LBound(a) To UBound(a)
        a(i) = a(i) - b(i)
    Next i
    decrement = a
End Function
Private Function increment(ByVal a As Variant, b As Variant) As Variant
    For i = LBound(a) To UBound(a)
        a(i) = a(i) + b(i)
    Next i
    increment = a
End Function
Private Function test(a As Variant, b As Variant)
    flag = True
    For i = LBound(a) To UBound(a)
        If a(i) < b(i) Then
            flag = False
            Exit For
        End If
    Next i
    test = flag
End Function
Private Function unfactor(x As Variant) As Long
    result = 1
    For i = LBound(x) To UBound(x)
        result = result * prime(i) ^ x(i)
    Next i
    unfactor = result
End Function
Private Sub compile(program As String)
    program = Replace(program, " ", "")
    programlist = Split(program, ",")
    For Each instruction In programlist
        parts = Split(instruction, "/")
        nf.Add factor(Val(parts(0)))
        df.Add factor(Val(parts(1)))
    Next instruction
End Sub
Private Function run(x As Long) As Variant
    n = factor(x)
    counter = 0
    Do While True
        For i = 1 To df.Count
            If test(n, df(i)) Then
                n = increment(decrement(n, df(i)), nf(i))
                Exit For
            End If
        Next i
        Debug.Print unfactor(n);
        counter = counter + 1
        If num = 31 Or counter >= halt Then Exit Do
    Loop
    Debug.Print
    run = n
End Function
Private Function steps(x As Variant) As Variant
    
    For i = 1 To df.Count
        If test(x, df(i)) Then
            x = increment(decrement(x, df(i)), nf(i))
            Exit For
        End If
    Next i
    steps = x
End Function
Private Function is_power_of_2(x As Variant) As Boolean
    flag = True
    For i = LBound(x) + 1 To UBound(x)
        If x(i) > 0 Then
            flag = False
            Exit For
        End If
    Next i
    is_power_of_2 = flag
End Function
Private Function filter_primes(x As Long, max As Integer) As Long
    n = factor(x)
    i = 0: iterations = 0
    Do While i < max
        If is_power_of_2(steps(n)) Then
            Debug.Print n(1);
            i = i + 1
        End If
        iterations = iterations + 1
    Loop
    Debug.Print
    filter_primes = iterations
End Function
Public Sub main()
    init
    compile ("17/91, 78/85, 19/51, 23/38, 29/33, 77/29, 95/23, 77/19, 1/17, 11/13, 13/11, 15/14,  15/2, 55/1")
    Debug.Print "First 20 results:"
    output = run(2)
    Debug.Print "First 30 primes:"
    Debug.Print "after"; filter_primes(2, 30); "iterations."
End Sub