formal parameter 'number' has different type when promoted
The type of the specified parameter is not compatible through default promotions with the type in a previous declaration.
For two function types to be compatible, the type of each parameter must be compatible with the type that results from application of the default argument promotion.
This is an error in ANSI C (/Za) and a warning when the Microsoft extensions (/Ze) are used.
The following example causes this warning:
void func();
void func(char); // warning, char promotes to int