Ok so I've got these 2 vectors, one containing Zombie objects, the other containing Bullet objects. I've got a function which checks for a collision between the 2, and then sets both objects' isDead value to true. Then, I run another loop that erases all the isDead objects from the vectors. There are 2 problems.
1. Bullets are never erased. If a bullet hits a zombie, it just continues on as though nothing happened.
2. Every time a bullet hits the last zombie on the screen (last zombie in vector) the program crashes.

Here's the function that checks for collision between each zombie and each bullet:

And here is the code in main() which erases dead objects:

for (std::vector<Bullet>::iterator i=bullet.begin(); i!=bullet.end(); i++)
    if (i->checkIfDead())
        bullet.erase(i);
         
for (std::vector<Zombie>::iterator i=zombie.begin(); i!=zombie.end(); i++;)
    if (i->checkIfDead())
        zombie.erase(i);

Sorry for just throwing up all this code, but I'm not sure what to do anymore. Thanks for any help

You don't want to erase while iterating over the vector. This is because it erasing an element invalidates all iterators. You could try using std::remove_if in the following way:

#include <algorithm>

bullet.erase(std::remove_if(bullet.begin(),
                             bullet.end(),
                             [](const Bullet& b) {return b.checkIfDead();}),
               bullet.end());

This uses a lambda function, so if you aren't working in c++11(you can enable it with the compiler flag -std=c++11), you'll have to find another way.

@#00JMP00: for, while and if-statements have the first statement after them implicitly in scope. You don't need braces if you only have one inner statement(though it is recommended in most coding style guidelines).

Solved it. While I imagine that the answers here would have probably fixed the issue, I think this solution works just as well. For anyone who wants to know, here is the new code:

for (std::vector<Bullet>::iterator i=bullet.begin(); i!=bullet.end(); i++)
{
    if (i->checkIfDead())
        bullet.erase(i);
    if (bullet.empty())
        break;
}

I dare say the bullet.empy() is redundant.

Anyway you're skipping checks due to the i++ in the for loop expression, as others have noted.

I use the swap´n pop method instead of using erase.

Example:

for(int i=0;i < myVec.size();i++){
if(condition){//collision or what ever
std::swap(myVec[i],myVec.back());
myVec.pop_back()
}
}

It is faster since C11.;)

You can erase from a vector while in a loop like this:

for (int i = 0; i != bullet.size(); i++)
{

    //update bullet here

    if (bullet[i]->checkIfDead())
    {
        bullet.erase(i);
        i--;
        continue;
    }
}

The continue isn't necessary if this if statement is at the end of the for loop, but if there's code after it the continue is recommended. Typically you put the erase code at the end of the for loop anyway.

I wish it were that easy, but sadly, the erase() function requires an iterator. Your code would give and error because you tried send it an int