First: the parameter of main isn't named. If there is no parameter, then it should be empty. Secondly the case statement has the wrong syntax.. It should be case <value>:
What?
No - wrong on both counts!
First:
A function declaration with an empty parameter list is not a prototype (just a declarator, see C11 ยง6.7.6.3, and specifically the examples in paragraph 16).
For a prototype to specify no parameters you MUST use void, as an empty parameter list makes no statement about the arguments the function takes.
In fact, this is perfectly standard C - but bad practice (and of course not MISRA compliant!):
int f();
int f(int i)
{
/* My function body */
}
Misra C makes an explicit note that for functions taking no arguments void must be used.
Second:
The syntax is not "case <value>:" and it's described in "6.8.4.2 The switch statement" as (paragraph 3):
The expression of each case label shall be an integer constant expression [...]
I hope you agree that (1) is a perfectly cromulent integer constant expression, as is e.g. (0xFF - 5*8 ).