# include <stdio.h>
/*
	This program, range, accepts 2 or 3 command line arguments
	and checks that they are integers. Range prints a range of
	numbers one per line on the standard output, starting with
	the first argument, incrementing (or decrementing) with the 
	third argument until the next number printed would be greater 
	(or lesser) than the second argument.
	If the third argument is missing, then the increment
	is set to 1 (similarly when the third argument is specified as
	zero). The absolute of the third argument is used as the
	increment, whereas the sign of the other arguments is never
	changed.

	Author:		Brett Jordan, CiTR
	Date created:	20 March 1991
*/

main(argc, argv)
int argc;
char *argv[];
{
	int	err, i, stnum, endnum, incr, *argi[3];

	err = 0;
	argi[0] = &stnum;  /* Make argis point to the final resting */
	argi[1] = &endnum; /* place of the command line arguments */
	argi[2] = &incr;

	/* if incorrect number of arguments ... */
	if (argc < 3 || argc > 4)
		err = 1;
	else {
		/* argc is the count of all words on the command line,
		   whereas argc-1 is the number of arguments, therefore
		   for all arguments ... */
		for (i=0; i<(argc-1); i++)
			/* increment argv to point to next argument,
			   initially pointing to 'range', and pass it
			   by value, pass argi element so that sscanf
			   can convert text into integer and place the
			   integer arguments in their final resting
			   places.  If sscanf returns 0 then there was
			   an error. */
			if (sscanf(*++argv, "%d", argi[i]) == 0) {
				err = 1;
				break;
			}
	}

	/* if an error occurred, print usage info */
	if (err != 0) {
		usage();
		return(1);
	}
	else {
		/* if no increment specified, or set to 0, make it 1 */
		if (i==2 || incr==0)
			incr = 1;
		/* ensure that increment is positive */
		if (incr < 0)
			incr = 0 - incr;

		/* if decrementing... */
		if (stnum > endnum) {
			for (i=stnum; i>=endnum; i-=incr)
				printf("%d\n", i);
		}
		/* if incrementing... */
		else {
			for (i = stnum; i <= endnum; i+=incr)
				printf("%d\n", i);
		}
		return(0);
	}
}


usage()
{
	printf("usage: range start end [increment]\n");
	printf("\n");
	printf("start, end and increment must be integers.\n");
}