Code that calculates Hailstone Sequence of input numbers, and code that calculates the number with the largest Hailstone sequence smaller than `z`

Question

I managed to make a simple function that calculates the Hailstone sequence of numbers and print it out, and I just done a calculator that grabs the number with the largest sequence smaller than n — and it may disprove the Collatz conjecture.

Code with input numbers:

#include <iostream>
#include <string>

using namespace std;

void parseSequence(long n, long o) {
    long m = n;
    if (m % 2 == 0) {
        m /= 2;
    }
    else if (m != 1) {
        m *= 3;
        m++;
    }
    cout << m << endl;
    if (m == 1) {
        cout << "End of sequence! (sequence's lenght is " << o << ")." << endl;
    }
    else {
        o++;
        parseSequence(m, o);
    }
}

int main() {
    string p;
    long n;
    cout << "\nWhich is the number to calculate the Hailstone sequence?\n";
    cin >> n;
    parseSequence(n, 1);
    cout << "Parse more sequence?\n\n(y|n)\n\n:";
    cin >> p;
    if (p == "y" or p == "Y") {
        return main();
    }
    else return 0;
}

Calculator that displays number's largest sequence lenght with it's sequence's lenght:

#include <iostream>
#include <string>

using namespace std;

int parseSequence(long n, long o) {
    long m = n;
    if (m % 2 == 0) {
        m /= 2;
    }
    else if (m != 1) {
        m *= 3;
        m++;
    }
    cout << m << endl;
    if (m == 1) {
        cout << "End of sequence! (sequence's lenght is " << o << ")." << endl;
        return o;
    }
    else {
        o++;
        return parseSequence(m, o);
    }
}

int main() {
    string p;
    long n;
    cout << "\nWhich is the max number to calculate the longest sequence?\n";
    cin >> n;
    long l;
    long q;
    long y;
    long i;
    q = 0;
    for ( i = 1; i <= n; i++) {
         l = parseSequence(i, 0);
         if (l > q) {
                q = l;
                y = i;
         }
    }
    cout << "The number with the largest sequence : It's sequence's lenght = " << y << " : " << q;
    return 0;
}

I call the last one Project LightyMoon.

Answer 1

Never call main recursively.

It is undefined behavior. Use a loop instead.

Don't use recursion excessively.

In the case of parseSequence recursion actually makes it harder to understand and perform much worse. Usually each step for recursion takes a little bit of memory - something you want to avoid in this case.

Use a loop instead, in this case a for loop.

Use meaningful variable and function names

parseSequence does not parse a sequence. In the current form computes one step of a sequence.

One character names are generally frowned upon. Use descriptive names such as length, etc..

Avoid using namespace std;

See https://stackoverflow.com/a/1452738/620382