Exercise 1-22 from The C Programming Language by Brian W. Kernighan, Dennis M. Ritchie​ "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. Make sure your program does something intelligent with very long lines, and if there are no blanks or tabs…

wrap80.c

#include <stdio.h>

/*
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. Make sure your program does something intelligent with very long lines, and if there are no blanks or tabs before the specified column.
*/

#define COLUMN_WIDTH 80
#define MAX_LINE 1000


main(){
	char currentWord[MAX_LINE];
	int i;
	for (i = 0; i < MAX_LINE; ++i)
		currentWord[i] = '\0';

	int c,length,pos;
	pos = 0;
	length =0;
	while((c = getchar()) != EOF){
		if(c == ' ' || c =='\t' || c =='\n'){
			//End buffered word
			currentWord[pos] = '\0';
			//Wrap word
			if(length + pos >= COLUMN_WIDTH){
				printf("\n");
				length = pos;
			}else{
				if( c == '\n')
					length=0;
				if( c == '\t')
					length = length + 4;
				else
					length++;
			}
			printf("%s",currentWord);
			putchar(c);
			pos = 0;
		}else{
			//Buffer word
			currentWord[pos] =c;
			++pos;
		}
		++length;
	}
}

To run:

$cc wrap80.c -o wrap
$$./wrap < somefiletowrap.txt > formatedfile.txt

Several errors with test input