hidden facts of printf() statement

printf() statement is used to print the message as well as values of the variable, but some hidden facts for printf() statements are:

1. The return type of printf() statement are integer i.e the number of character printed by the printf statement.
     Example:  printf("%d","printf("Hello")); will print 5
2. If we do not provide variable name with the printf statement like printf("%d"); , Then the printf statement print the value which is in top of the stack of the memory.
    Example:
    void main()
    {
         int a=100,b=78;
         printf("%d");
}
you feel that it is the wrong or syntax error, but it will print the latest value which is on top of the stack that is 78