Passing parameters to functions

• a sequence of expressions are separated by commas, as in:
  a = average3( 12 * 45, 238, x - 981 );

• each of these expressions has a datatype. In the above example, each of the expressions in an int.
• when the function is called, the expressions are evaluated, and the value of each expression is assigned to the parameters of the function:

  float average3( int x, int y, int z ) { return (x + y + z) / 3.0; }

• during the execution of the function, the parameters are local variables of the function.

They have been initialized with the calling values (x = 12 * 45 ...), and the variables exist while the function is executing.
They "disappear" when the function returns.
• Quite often, functions require no parameters to execute correctly. We declare such functions with:

  void backup_files( void ) { ..... }

  and we just call the functions without any parameters: backup_files();