c - Non-static variable initialization

Question

I'm reading a book C progaming faq's. Here is passage of the book

Automatic variables are variables defined inside a function or block of code without the static keyword. These variables have undefined values if you don’t explicitly initialize them. If you don’t initialize an automatic variable, you must make sure you assign to it before using the value.

Here is my code:

#include <stdio.h>
int main (int argc, const char * argv[])
{    
    {
        int x;
        printf("%d", x);
    }
}

The result of printf is 0. Why is the variable initialized?

Answer 1

For static and global variables it is 0; automatic variables are not initialized by default.

in the c language there is no default value for non static local variables. The variable holds whatever was in memory before it became a variable. It's best to always initialize a non static local variable before using it in the c language (or at least before comparing it to something else). Also It's best to assume that there is no default value because this varies from language to language, and hardware to hardware.

Read more: http://wiki.answers.com/Q/What_is_the_default_value_of_integer_in_c#ixzz1iaij7hRK