Most people don't know that these function declarations
int foo();
int bar() { }
do not declare a prototype for foo respectively bar. In consequence, this is a legal implementation of foo:
int foo(int a) { }
And this is a likely illegal call to bar, however the compiler can't warn:
bar(42);
To provide a prototype, add void inside the parenthesis to make it a parameter-list (instead of the C89 identifier list) and all of the above would yield compile time errors:
int foo(void);
int bar(void) {}
This is due to Cs history of K&R style function declarations and definitions:
int foo();
int foo(a)
int a;
{
/* do something */
}
Compatibility is great, but I don't think you should go lower than C99 if not explicitly needed.