Exercise 7.2 - print non-graphic characters in octal or hexadecimal¶

/**
 * Write a program that will print arbitrary input in a sensible way. As a
 * minimum, it should print non-graphic characters in octal or hexadecimal
 * according to local custom, and break long text lines.
 */

#include <ctype.h>
#include <stdio.h>

#define MAXLINE 100 /* maximum number of chars in one line */
#define OCTLEN 6    /* length of an octal value */

const char *input = "This\tis\ta\ttest.   With a   very   long line.";
int input_index = 0;

int _getchar(void) {
    if (input[input_index] == '\0') {
        return EOF;
    } else {
        return input[input_index++];
    }
}


/* inc : increment position counter for output */
int inc(int pos, int n) {
    if (pos + n < MAXLINE)
        return pos + n;
    else {
        putchar('\n');
        return n;
    }
}

/* print arbitrary input in a sensible way */
int main(void) {
    int c, pos;

    pos = 0; /* position in the line */

    while ((c = _getchar()) != EOF)
        if (iscntrl(c) || c == ' ') {
            /* non-graphic or blank character */
            pos = inc(pos, OCTLEN);
            printf("\\%03o", c);
            /* newline character */
            if (c == '\n')
                pos = 0;
            putchar('\n');
        } else {
            /* graphic character */
            pos = inc(pos, 1);
            putchar(c);
        }
    return 0;
}