Hi,
I have a project with a main.ino file that is trying to include some old regular C files ive made (with Add|Add new C item)   myUart.c and myUART.h

In the .h file i have
void myUartInit();

In the .c file i have
void myUartInit()
{
Serial.begin(57600);
}

and when i in my .ino file call the myUartInit() i get 
error: 'Serial' undeclared (first use in this function)
and i have #include "myUart.h" in the ino file!

i have tried to include following libraries in myUart.c without success, i only get more errors
#include <MinimumSerial.h>
#include <USBAPI.h>
#include <HardwareSerial.h>

Any suggestion on what im doing wrong, many thanks in advance. I really would like to have the old AVR studio 4 layout of splitted files in this manner.

You are right the .c files are not where you want to be.

It's up to you if you use .ino or cpp. 

.ino is easier for some people because prototypes are made automatically and all code/vars/functions/includes are shared between all .ino files. 

Thanks