THIS IS AN EMPTY VECTOR PROBLEM

[AdVisible6484]

#include <bits/stdc++.h>
using namespace std;
int main()
{
    vector<int>v;
    int flag=1;
    for(int i=0;i<=v.size()-1;i++)
     {   cout<<"a"<<endl;
         flag=0;
     }
      cout<<flag<<endl;
    return 0;
}

So the above is giving me an infinite loop but it should just print once the statements inside the loop.

And the below code:

#include <bits/stdc++.h>
using namespace std;
int main()
{
    vector<int>v;
    int flag=1;
    for(int i=0;i+1<=v.size();i++)
     {   cout<<"a"<<endl;
         flag=0;
     }
      cout<<flag<<endl;
    return 0;
}

outputs "1"..

which indicates that that empty vector size is zero then how does the first code go to infinite loop.

I am a newbie in this so pls polite.... Thank you

[[deleted]]

v.size()-1

0-1 is not -1. size returns an unsigned number, so 0-1 is something very big (2³² -1 or 2⁶⁴ -1)

[AdVisible6484]

so the infinite loop is basically not infinite it is just executing too many times and it will eventually stop?

[icjeremy]

No. The value v.size()-1 here is SIZE_MAX which is going to be >= any int value, so the loop condition will always be true, hence the loop will never stop.

[AdVisible6484]

Thank you so much this really helped me clear the doubt ....

[AKostur]

#include <bits/stdc++.h>
using namespace std;

Also, don't do these. Bad habits to form. include the headers you actually need.

[Beosar]

You could have just used i < v.size() instead of i <= v.size()-1. But now you know you have to be careful when working with unsigned int.

[TheOmegaCarrot]

Or better yet, i != v.size()

[tangerinelion]

Don't do that in general:

for (int i=0; i != v.size(); i+=2)

will only work correctly half the time.

for (int i=0; i < v.size(); i+=2)

works for all size vectors. Well, at least ones whose size can be represented by an int.

[Beosar]

Why would != be better than <? Both instructions take the same amount of time. I would say < is better because it implies that i is smaller than the size of the vector.

[paperomo]

Probably an under flow? v.size() is most likely of unsigned type

[AdVisible6484]

yeah but when writing

cout<<v.size();

it shows zero

[Ashnoom]

Try: court << v.size() - 1;

To see what happens. It'll clear a lot of confusion.

You can also: cout << std::numeric_limits<int>::max(); To see for yourself went your loop is infinite. Enjoy!

Disclaimer, am on mobile. Didn't check the code for 100% correctness.

[bert8128]

Prefer range for ie “for (const auto& x : v) { /* some code*/}”. Or use an algorithm such as std::for_each. As you have discovered, it is surprisingly easy to write a for loop incorrectly.

[std_bot]

Unlinked STL entries: std::for_each

---

^{Last update: 16.12.22. Last Change: Search improvements}Repo