Nested variable declarations using the same name

Hi, I was wondering what is the point of the language supporting
nested variable declarations of the same name?

For example:

int a = 0;

if( some_bool )
{
     int a = 5;
     ...
}

cout << a;  //this outputs 0


I can't think of a reason why this would be supported, and I feel the
compiler should throw a warning. So, is there a good useful reason to
allow this?

Thanks.

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