Why is this printing '4232078'?

Question

#include <iostream>
using namespace std;

class MyClass {
private:
int myVar;
public:
MyClass(int a){
a = myVar;
}
int getMyVar(){
return myVar;
}
};

int main() {
MyClass myObj(7);
cout<<myObj.getMyVar()<<endl;
}

Answer 1

As for the "mysterious value" :-

https://stackoverflow.com/questions/4137239/garbage-values-in-c-c

Answer 2

Because you don't give myVar value, so it's value is random.
Your bug is at line 9. You should write "myVar=a" if you want the answer is 7.
Hope I have answered your question.

Answer 3

I'll try this out in CodePlayground (FYI, if you add a link to your codes there for visitors/comments that's super useful)

Answer 4

Expanding on Hatsy's answer (because it's nice to see how things are allocated):

When c++ initializes your object, it creates a data structure in memory with the size of its internal variables. Your class (static or instantiated) is 4 bytes long, so each instance (with its uninitialized int myVar) gets 4-bytes of what was there before.

It is interesting that "what was there before" is a constant across submissions (and across all runtime servers; I ran this a lot). Determinism implies that it's left over from the wrapper, compiler or bootstrapping process itself (which may or may not be a security concern).

The actual constant value is different below because my debugging shifted the allocation address, but it's the same question / in the same vicinity (and notice how my two copies of the object are allocated 4 bytes apart):

https://code.sololearn.com/crkEJL64XKLG/?ref=app

Answer 5

Turns out "a = myVar" was the issue. Needed to be flipped: "myVar = a". Didn't realize the order mattered, but it makes sense: myVar is receiving a new assignment/value, so it needs to be on the left.

Still no idea what the mysterious number is...

Answer 6

Thanks, Kirk. Didn't know I could do that. I'll do as you say in future!

Answer 7

Okay, so I added "return 0;" to the main function, but it's still printing this weird number. Where's it getting that from? It's especially strange because a nearly identical practise code I used seems to work just fine at printing '32', as specified in its code:

#include <iostream>
using namespace std;

class MyClass {
public:
MyClass(int a) {
var = a;
}
int getVar() {
return var;
}
private:
int var;
};

int main() {
MyClass myObj(32);
cout<<myObj.getVar()<<endl;
return 0;
}