what is the purpose of using void keyword

[farheen]

What is the main purpose of using void keyword

[weaknessforcats]

In C you cannot have multiple functions with the same name. Like this:

int Area(Circle* x);
int Area(Square* x);
int Area(Triangle* x);

The workaround is to use a void pointer. The keyword void just means "no-type". The you supply a second argument to explain the void pointer:

int Area(void* x, int y);

May y=1 means the x argument is a Circle whereas y = 2 may mean the x argument is a Square.

This allows the function to typpecast the void* to the correct type and do the calculation.

This situation does not arise in C++ where function names are identitifed by their signature and not by their names.

The other place you see void is as a function return type:

void func(int arg);

This tells the compiler that no type is returned making this an error:

int val = func(10);

Without the void return, the function is assumed to return an int. Now the code passes the compile OK but crashes at run time when val is garbage.

[donbock]

A void* pointer can be assigned a value that points to any data type. You should not assign a function pointer value to it.

This function prototype declares a function that takes no arguments. You will get a compiler error if you pass any arguments to it.
int func(void);

Notice that this declaration is different than the previous case.
int func();
In this case, there is no function prototype. The compiler will allow any number of arguments of any type.

You can cast a statement to void to instruct the compiler that you are intentionally discarding the value of the statement. You get the same effect whether you cast to void or not. I suppose the point of being explicitly intentional is to make your intentions clear to the next person to read your code; doing so may also prevent some compiler warnings. Some examples of this usage:
(void) printf("%d\n", var);
(void)0;

That last one is an idiom that shows up from time to time when you want a statement that does nothing. You almost always want your statements to do something, so this idiom is only seen in very uncommon special situations.