Range of float id -2.25e-308 to 2.25e+308

Is there any difference in the following declarations?
int myfun(int arr[]);
int myfun(arr[20]);

Suppose a program is divided into three files f1, f2 and f3, and a variable is defined in the file f1 but used in files f2 and f3. In such a case would we need the extern declaration for the variables in the files f2 and f3?

Global variable are available to all functions. Does there exist a mechanism by way of which it available to some and not to others.

Is it true that a global variable may have several declarations, but only one definition?

Is it true that a function may have several declarations, but only one definition?

The way the break is used to take control out of switch and continue to take control of the beginning of the switch?

Can we use a switch statement to switch on strings?

We want to test whether a value lies in the range 2 to 4 or 5 to 7. Can we do this using a switch?

By default, the data type of a constant without a decimal point is int, whereas the one with a decimal point is a double.