what is the return type of printf [closed]

Answer 1

What you probably read "you need a l-value to accept the return of a function call"

For eg. in your code.

you cannot do

5 = fun();

because 5 is not an l-value.

However both of these are fine

int i;
i = fun(); // i is an l-value

or

fun(); // ignore the return value

Also, you need

char * str = "hello"; // you cannot allocate a string to a single char

And void main() is non-standard.

You need

int main()

Answer 2

The function fun() is returning an int, you are just not assigning it to anything. So the return value is being discarded as it is not assigned to anything.

printf by the way, is not a void function but returns the number of characters printed, which is 5 in case of "Hello".