Why do I get this unexpected result using atoi() in C?

I don't understand the results of the following C code.

main()
{
    char s[] = "AAA";
    advanceString(s);
}

void advanceString(p[3])
{
    int val = atoi(p);
    printf("The atoi val is %d\n",val);
}

Here the atoi value is shown as 0, but I could not figure out the exact reason. As per my understanding, it should be the summation of decimal equivalent of each values in the array? Please correct me if I am wrong.