Function Declarations, Function Calls, and Function Implementations

• Function Declaration (Prototype):
  return_data_type function_name( parameter_list);
• The return_data_type may be any built-in data type or user defined data type. A void return_data_type indicates that the function will not return any values. If a return_data_type is omitted, it implies an int will be returned by the function
• The function_name can be any valid (non-keyword) identifier. main is a special function that identifies the beginning of the program
• The parameter_list is a comma separated list of data types that will be provided to the function when it is called
• Variable names need not be specified in the parameter_list, only their data types are required


• Function Calls:
  function_name(actual_parameter_list);
• The return_data_type is not specified in a function call
• The actual_parameter_list are the comma seperated values of the variables to be used as arguments by the function. This is also called the call by value method of invoking a function.
• After the execution of the function, the returned value replaces the function call, when it is used in an expression
• The order of the data types in the actual_parameter_list should be consistent with the order specified in the function declaration


• Function Implementation:
  return_data_type function_name(formal_parameter_list)
  {//The body of the function goes here...}
• The function implementation begins with a function header
• The function header specifies the return_data_type, function_name, formal_parameter_list. The function header is not terminated with a semicolon
• The formal_parameter_list is a comma separated list of variables (and their data types). These variables have local scope in the function
• The actual parameters from the function call get 'mapped' onto their corresponding formal parameters
• The function body must be terminated by a return statement, which returns a data value of the same type as that specified in the function declaration and the function header
• Only one value may be returned


• Example ...