While in Java, for example, you get an error if you want to run a function which contains a variable that hasn't been initialized  java: variable x might not have been initialized , not so in C++ and that can be tricky.

In C++ variables which haven't been initialized get random values which can or will almost always lead to unexpected results.

C++ example:

int main() {
        int x = 15;
        int y;
        int z = x + y;
        cout << z ;
}
// leads to a result of...
82
Process finished with exit code 0

So - ALWAYS INITIALIZE variables when programming in C++ !