C: type conversion when passing an argument on a function call

Question

From The C Programming Language 2nd Edition:

Since an argument of a function call is an expression, type conversions also take place when arguments are p

Answer 1

The compiler is complaining that it assumed function_call is an int returning function as indicated by the standard, and then you tell it is a void function. The compiler won't care about arguments unless you are explicitely declaring them to be different to the actual function. You can pass it no arguments and it won't complain.

You must always declare your functions because this error will go undetected if the function is in other modules. If the function should return any type that could be larger than int such as void* or long, the cast to int in the caller function will most likely truncate it, leaving you with a weird bug.