/*
 * a more complicated program with function pointers
 *
 * Matt Bishop, ECS 36A
 * -- May 22, 2024	original version
 */
#include <stdio.h>
#include <ctype.h>
#include <string.h>

/*
 * first function: make everything upper case
 */
char *upper(char *str)
{
	static char buf[1024];	/* buffer to return transformed string */
	char *b;		/* pointer to go through buf */

	/* change all lower case letters to upper case */
	for(b = buf; *str; b++, str++)
		*b = toupper(*str);
	
	/* return the internal. saved buffer */
	return(buf);
}

/*
 * second function: make everything lower case
 */
char *lower(char *str)
{
	static char buf[1024];	/* buffer to return transformed string */
	char *b;		/* pointer to go through buf */	

	/* change all upper case letters to lower case */
	for(b = buf; *str; b++, str++)
		*b = tolower(*str);
	
	/* return the internal. saved buffer */
	return(buf);
}

/*
 * the main function
 */
int main(void)
{
	char inbuf[1024];	/* input buffer */
	char *pin;		/* used to scan the input buffer */
	char *(*func)(char *);	/* pointer to function to call */

	/*
	 * loop, transforming the input
	 */
	while(printf("l/u/EOF> "), fgets(inbuf, 1024, stdin) != NULL){

		/* fgets keeps the newline; we don't want it */
		if (inbuf[strlen(inbuf)-1] == '\n')
			inbuf[strlen(inbuf)-1] = '\0';

		/* skip any leading white space */
		pin = inbuf;
		while(isspace(*pin))
			pin++;

		/* got a char -- interpret command */
		/* note a NUL byte means nothing;  */
		/* go back and ask again           */
		switch(*pin++){
		case '\0':		/* NUL byte -- ignore line */
			continue;
		case 'u':		/* transform to upper case */
		case 'U':
			func = upper;
			break;
		case 'l':		/* transform to lower case */
		case 'L':
			func = lower;
			break;
		default:		/* remind the user of good commands */
			printf("Commands: l, u, EOF\n");
			continue;
		}
		
		/* now skip any intervening space */
		while(isspace(*pin))
			pin++;

		/* if there's no string, remind the user */
		if (*pin == '\0'){
			printf("input: [u | l] string or EOF\n");
			continue;
		}

		/* do the transformation and print the result */
		printf("'%s' becomes '%s'\n", pin, (*func)(pin));
	}

	/* bye! */
	return(0);}