Причина, по которой переменная производительность непредсказуема без начального значения?

I want to know why if we name a variable and name it n and set it to the main function.  Why is the result unpredictable when I call that variable in another block?

why once the program gave an error and once with random numbers?

#include<iostream>
using namespace std;
int main()
{
	int n=44;
	{
		int n;
		cout<<"n="<<n;
		}		
return 0;	
}