Why I got garbage value after reclaring variable in a smaller scope

Question

        int tar = 0;
        {
            int tar = tar;
            cout<<tar;       
        }

It prints out 814005873, but what I expected was 0.

Answer 1

The variable in the outer scope is not relevant. You'd get the same with

    {
        int tar = tar;
        cout<<tar;       
    }

tar is not initialzed hence using its value to initialize itself is undefined behavior. All major compilers warn about such case of tar being used uninitialized. For example: https://godbolt.org/z/3x437P46K. Don't ignore warnings!

It may look weird that this isnt an error, but for a custom type such initialization can be meaningful. For example:

struct foo {
    foo& other;
    foo(foo& other) : other(other) {}
};

int main()
{
    foo f = f;
}

f holds a reference to itself.