gcc - Miscellaneous functions undergo implicit conversions in C?

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65860165/miscellaneous-functions-undergo-implicit-conversions-in-c

Answer 1

The variable arguments to scanf and printf will only undergo the default argument promotions. This means that arguments of type float are promoted to type double and integer types smaller than int will be promoted to int. Note that this does not apply to pointers.

In the case of scanf, the %d format specifier is expecting an int * but you're passing in an unsigned char *. These types are not compatible so you have undefined behavior.

In the case of printf, %d expects an int. The unsigned char you're passing in gets promoted to int so in this case it is valid.