What is the difference between initialisation and definition in C programming?

Answer 1

Variable-declaration is:

extern int x;

extern double y;

extern char a;

Variable-definition is:

int x;

static double y;

auto char a;

Variable-definition with initialization is:

int x = 1;

static double y= 2.3;

auto char a = 'w';

Answer 2

A discussion of initialization and definition should also include a discussion of declaration.

Declaration is the point in compilation where an object is described to the compiler. At that point, the compiler knows the type and size of the object.

Definition is the point in compilation where an object is allocated by the compiler. At that point, the compiler knows the address of the object.

Initialization is the point in compilation where an object is assigned an initial value. At that point, the compiler knows the value of the object.