I am a little surprised by the following.
Example 1:
char s[100] = \"abcd\"; // declare and initialize - WORKS
Example 2:
When initializing an array, C allows you to fill it with values. So
char s[100] = "abcd";
is basically the same as
int s[3] = { 1, 2, 3 };
but it doesn't allow you to do the assignment since s is an array and not a free pointer. The meaning of
s = "abcd"
is to assign the pointer value of abcd to s but you can't change s since then nothing will be pointing to the array.
This can and does work if s is a char* - a pointer that can point to anything.
If you want to copy the string simple use strcpy.