Ex_1.22_fold.c

/* Exercise 1-22: Write a program to "fold" long input lines into two or more
		  shorter lines after the last non-blank character that occurs
	          before the n-th column of input. */
				  
#include <stdio.h>


#define MAXCOL 		35				/* folded line length */
#define TABVAL 		8				/* standard tab length */
#define CURTAB(c) 	(TABVAL - ((c) % TABVAL))  	/* current tab size */
#define NO_BLANK	-1				/* signifies no blank found */

int lastblank(const char arr[], int len);

/* folds long input lines into two or more shorter lines */
int main(void)
{
	int c;			/* character variable */
	int i, j;		/* indexing variable(s) */
	int pos;		/* current position in array */
	int col;		/* current column of output */
	int lbc;		/* last blank character position */
	char line[MAXCOL + 1];	/* fold array */
	
	pos = col = 0;
	while ((c = getchar()) != EOF) {
		/* process line array, keep track of line length by columns */
		line[pos++] = c;
		col += (c == '\t') ? CURTAB(col) : 1;

		/* create fold */
		if (col >= MAXCOL || c == '\n') {
			line[pos] = '\0';
			
			if ((lbc = lastblank(line, pos)) == NO_BLANK) {
				/* split word if no blank characters */	
				for (i = 0; i < pos; ++i)
					putchar(line[i]);
				/* reset column value and array position */
				col = pos = 0;
			}
			else {
				/* print array up until last blank character */
				for (i = 0; i < lbc; ++i)
					putchar(line[i]);
				/* feed remaining characters into buffer */
				for (i = 0, j = lbc + 1, col = 0; j < pos; ++i, ++j) {
					line[i] = line[j];
					/* set new column value */
					col += (c == '\t') ? CURTAB(col) : 1;
				}
				/* set array position after remaining characters */
				pos = i;
			}
			/* finish folded line with newline character */
			putchar('\n');
		}
	}
	
	return 0;
}

/* finds the last whitespace character in an array
   and returns the position */
int lastblank(const char arr[], int len)
{
	int i, lbc;
	
	lbc = -1;
	for (i = 0; i < len; ++i)
		if (arr[i] == ' ' || arr[i] == '\t' || arr[i] == '\n')
			lbc = i;
	
	return lbc;
}