Program error (occurs when sending bigger numbers to function with vector)

[sknn]

Hello, I'm trying to solve problem 14 from projecteuler (Longest Collatz sequence). It's my first try so probably the code or program is not good at all.
I need to check numbers from 13 to 1000000 and when I check from 13 to 100000 everything works fine except the lagg. But if I try to check from 13 to 200000 I get crash. I just cannot understand what is wrong. I would appreciate to get help with my program if possible but not an answer to this problem 14.

#include<iostream>
#include <vector>
using namespace std;

int collatzSequence(int num) {
    vector<int> chain;
    chain.push_back(num);
    int temp;
    while (num != 1) {
        if (num % 2 == 0) {
            num /= 2;
            chain.push_back(num);
        } else if (num % 2 != 0) {
            num = (num * 3) + 1;
            chain.push_back(num);
        }
    }
    return chain.size();
}

int main() {
    int stnum = 12;
    int chain = collatzSequence(12);
    for (int i = 13; i < 100000; i++) { // OK
    //for (int i = 1; i < 200000; i++) { // CRASH
        if (collatzSequence(i) > chain) {
            chain = collatzSequence(i);
            stnum = i;
        } else if (i > stnum && chain == collatzSequence(i)) {
            stnum = i;
        }
    }
    cout << stnum << " "  << chain;
}

By the way this number also does not work and crashes when I call my collatzSequence function on it alone

cout << collatzSequence(113383);

[o3hC5Di1]

Hi there,

Some pointers:

#include<iostream>
#include <vector>
using namespace std;

int collatzSequence(int num) {
    vector<int> chain;
    chain.push_back(num);
    int temp;
    while (num != 1) {
        if (num % 2 == 0) {
            num /= 2;
            chain.push_back(num);
        } else if (num % 2 != 0) {
            num = (num * 3) + 1;
            chain.push_back(num);
        }
    }
    return chain.size();
}

int main() {
    int stnum = 12;
    int chain = collatzSequence(12);
    for (int i = 13; i < 100000; i++) { // OK
    //for (int i = 1; i < 200000; i++) { // CRASH
        if (collatzSequence(i) > chain) {
            chain = collatzSequence(i);
            stnum = i;
        } else if (i > stnum && chain == collatzSequence(i)) {
            stnum = i;
        }
    }
    cout << stnum << " "  << chain;
}

- In main() you are calling your function 3 times. As this is a pretty expensive function to run, it would bee wise to run it once and store the result for future reference:

for (int i = 13; i < 100000; i++) { // OK
        int collatz = collatzSequence(i);
        if (collatz > chain) {
            chain = collatz;
            stnum = i;
        } else if (i > stnum && chain == collatz) {
            stnum = i;
        }

- You should probably try and use unsigned long long instead of int. You need to be careful with (signed) integers and the numbers you use. Often a problem that occurs onlyif a number is above a certain number it is caused by integer overflow.

Hope that helps, please do let us know if you have any further questions.

All the best,
NwN
}[/code]

[sknn]

thank you, NwN. Int was the problem there as you said. Changed it
int collatzSequence(unsigned long long num) { and no more errors occured.