f_FLAG
if (f[f_FLAG] == NULL)
file = fopen(f[f_FLAG], "r");
perror(f[f_FLAG]);
if (f[f_FLAG] == NULL)
fi = fopen(f[f_FLAG], "w");
perror(f[f_FLAG]);
f[f_FLAG] != NULL && f[t_FLAG] != NULL ||
argc == 2 && (f[f_FLAG] != NULL || f[t_FLAG] != NULL)) {
if (f[d_FLAG] != NULL || f[f_FLAG] != NULL)