Paragraph alignment problem

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define print_space printf(" ")

enum { maxlen = 1000000 };

int K;
char s[maxlen+1];
int spaces, ln;

void clenup(void)
{
    s[0] = 0;
    spaces = ln = 0;
}

void format_string(void)
{
    if(spaces == 0)
    {
        printf("%s", s);
        int i;
        for(i = ln; i < K; i++)
            print_space;
        printf("\n");
        clenup();
        return;
    }

    int space_size = (K-ln) / spaces,
      extra_spaces = (K-ln) % spaces;

    char *c;
    for(c = s; *c; c++)
    {
        putchar(*c);
        if(*c == ' ')
        {
            int i;
            for(i = 0; i < space_size; i++)
                print_space;
            if(extra_spaces)
            {
                print_space;
                extra_spaces--;
            }
        }
    }
    printf("\n");
    clenup();
}

int main(void)
{
    scanf("%d", &K);
    clenup();
    char new_word[K];
    while(scanf("%s", new_word) != EOF)
    {
        if(ln)
            if(ln + 1 + strlen(new_word) > K)
                format_string();
        if(ln)
        {
            strcat(s, " ");
            spaces++;
            ln++;
        }
        strcat(s, new_word);
        ln += strlen(new_word);
    }
    if(ln)
        format_string();
    return 0;
}