In the C language, a value passed to a function is called either an “argument” or a “parameter,” depending on viewpoint. From the viewpoint of the statement that calls the function, the value is an argument. In the view of the function receiving it, the value is a parameter.
Thus, in BEEPER1.C, the following function call passes an argument to the beep function:
beep( 5 );
Looking at the same value from the receiving end, the header of the beep function declares a parameter named num_beep as follows:
void beep( int num_beep );
The argument and parameter refer to the same value—in this case, the value 5. The naming distinction is just a matter of viewpoint, similar to the way you call a letter outgoing mail if you're sending it, or incoming mail if you're receiving it.