initial value of int array in C

If the array is declared in a function, then the value is undefined. int x[10]; in a function means: take the ownership of 10-int-size area of memory without doing any initialization. If the array is declared as a global one or as static in a function, then all elements are initialized to zero if they aren't initialized already.

As set by the standard, all global and function static variables automatically initialised to 0. Automatic variables are not initialised.

int a[10];  // global - all elements are initialised to 0

void foo(void) {
    int b[10];    // automatic storage - contain junk
    static int c[10]; // static - initialised to 0
}

However it is a good practice to always manually initialise function variable, regardless of its storage class. To set all array elements to 0 you just need to assign first array item to 0 - omitted elements will set to 0 automatically:

int b[10] = {0};