Declaration tells the compiler about a variable's name and type (e.g., 'extern int x;'). Definition actually allocates memory (e.g., 'int x = 5;'). A variable can be declared multiple times but defined only once.

Array name decays to pointer. p[5] is equivalent to *(p+5) which is *(arr+5) or arr[5]. This demonstrates pointer arithmetic.

When static is used with a global variable, it restricts its scope to the file where it is declared. Without static, global variables are accessible across files using extern.

p is a pointer storing the address of a. *p (dereferencing) gives the value at that address, which is 5. So both a and *p print 5.

When an array is passed to a function in C, it decays to a pointer pointing to the first element. This is why changes made in the function affect the original array.

typedef creates an alias (synonym) for existing data types. For example, 'typedef int Integer;' creates 'Integer' as an alias for 'int'. This improves code readability and portability. It doesn't create entirely new types, but provides alternative names.

The correct syntax is 'void function(void);' where 'void' in parentheses explicitly states no parameters. Option B is also valid in C (defaults to no parameters), but option A is more explicit and portable across C standards.

Structure allocates separate memory for each member (total size = sum of all members). Union shares a single memory location among all members (total size = size of largest member). This is a fundamental difference in memory allocation.

x++ is post-increment (returns 5, then x becomes 6), ++x is pre-increment (x becomes 7, then returns 7). The order of evaluation in printf is implementation-dependent, but typically right to left, giving 5 7.

In C, identifiers can only contain alphanumeric characters (a-z, A-Z, 0-9) and underscores (_), and must start with a letter or underscore. The dollar sign (\() is not allowed, making 'my\)var' invalid.