5.17 Functions

5.17 Functions

• Call by value, not reference.
• "C"s subprograms are functions.
• Functions may be recursive.
• Functions may not be defined within other functions.
• Functions have the form:

  return-type function-name  ( argument declarations )
  {
     declarations and statements
  }
  

• If the return type is not specified, it will return an int. If you don't want this, set the return-type to void.
• A function should have a prototype before the function is called. #include the necessary header (.h) files.
• Use the ANSI style of function definition. DO NOT use the original "C" language style.. (Well, at least stick to one of them.)

  A demonstration program with a prototype for rain and rain and functions main and spain.

  /* Program to demonstrate different function
   * prototypes and declarations 
   *
   * Louis Taber   Feb 11, 2001   PCC    
   */
  
        /* library prototypes and macros */
  #include <stdio.h>    
  
  double rain(double x, int y);
  void   cain(int r, int s);
  
  int   /* You may want the function name in Col #1 */
  main(int argc, char * argv[ ], char * env[ ])
  {
  return 0;
  }
  
        /* You can put them on seperate lines */
        /* old style                          */
  int spain(argc, argv, env)   
  int argc;
  char * argv[ ];
  char * env[ ];
  {
  return 0;
  }
  
  
  

  .

  I not quite sure why you would want it but it is available by anonymous ftp at:
  ftp://lt.tucson.az.us/pub/c/prototypes.c.

• main function revisited.

  The following program prints out the passed arguments and the environment variables. According to ANSI "C" Standard 9899 5.1.2.2.1 p 12 the only arguments passed to main are int argc and char *argv[ ]. Passing the environment is a UNIX extension.

  /* Program to print arguments to a program    */
  /* and the passed environment                 */
  /* L Taber   March 28, 1993   PCC             */
  
  #include <stdio.h>
  
  main(int argc, char * argv[ ], char * env[ ])
  
  {
  int i;
  
  /* Print number of arguments and the first argument */
  
  printf("argc = %d   File name = %s\n", argc, argv[0]);
  
  /* Print all remaining arguments - if any */
  
  for ( i=1; i<argc; i++) 
    printf(" arg[%d] = %s \n" ,i,argv[i]);
  printf("\n");
  
  /* Print the environment - if any */
  
  for ( i=0; env[i] != NULL; i++) 
    printf(" env[%d] = %s\n" ,i,env[i]);
  printf("\n");
  
  return 0;
  }
  

5.17 Functions