>>58
#include <stdio.h>
int main(void)
{
    FILE *fabc, *fa, *fb, *current;
    int c, prev;
    if (!(fabc = fopen("abc.txt", "r"))
            || !(fa = fopen("a.txt", "w"))
            || !(fb = fopen("b.txt", "w")))
        return fputs("can't open files\n", stderr), 1;
    current = fb;
    for (prev = '\n'; (c = getc(fabc)) != EOF; prev = c) {
        if (prev == '\n' && c == '&') current = fa;
        else if (prev == '\n') current = fb;
        putc(c, current);
    }
    fclose(fabc), fclose(fa), fclose(fb);
    return 0;
}