K&R Exercise 1.21 - c

Question

Currently struggling to solve ex 1.21. The task is: Write a program entab that replaces strings of blanks by the minimum number
of tabs and blanks to achieve the same spacing. Use the same tab stops as for detab . When
either a tab or a single blank would suffice to reach a tab stop, which should be given
preference?
Below is my code i have made so far. I have no problems typing the amount of spaces less than tabsize but when it is bigger than that I get segmentation fault. Could anyone help me, please?
#include <stdio.h>
#include <ctype.h>
#define TAB 8
#define MAXLINE 1000
int getmine(char s[], int lim);
int entab(char output[], int pos, int space);
int main()
{
char line[MAXLINE], output[MAXLINE];
int i;
while ((i = getmine(line, MAXLINE)) > 0)
{
int space = 0;
int pos = 0;
int count = 0;
while (line[count] != '\n')
{
if (line[count] != ' ')
{
space = 0;
output[count] = line[count];
}
else if (line[count] == ' ')
{
pos = count - space;
space++;
if (line[count + 1] != ' ')
{
if (space > TAB)
{
int z = entab(output, pos, space);
count = z;
}
else
{
for (int a = 0; a < space; a++)
output[pos + a] = ' ';
}
}
}
count++;
}
if (line[count] == '\n')
{
output[count] = line[count];
count++;
}
output[count] = '\0';
printf("%s", output);
}
}
int getmine(char s[],int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == '\n')
{
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
int entab(char output[], int pos, int space)
{
int nTabs = 0;
int nSpaces = 0;
int x = TAB - (pos % TAB);
if (x > 0)
{
output[pos] = '\t';
space = space - x;
nTabs = space / TAB;
nSpaces = space % TAB;
for (int a = 0; a < nTabs; a++)
output[pos + 1 + a] = '\t';
for (int b = 0; b < nSpaces; b++)
output[pos + 1 + nTabs + b] = ' ';
return pos + nTabs + nSpaces + 1;
}
else if (x == 0)
{
nTabs = space / TAB;
nSpaces = space % TAB;
for (int a = 0; a < nTabs; a++)
output[pos + a] = '\t';
for (int b = 0; b < nSpaces; b++)
output[pos + nTabs + b] = ' ';
return pos + nTabs + nSpaces;
}
}

Answer 1

Because the whitespace sequences of 8 characters are replaced by a single character (the tab), the number of read bytes from the input do not match to the written bytes in the output. A simple solution for this, is to simply keep track of two variables, one for the read bytes from the input, and one for the written bytes to the output. You could do this somewhat neater with pointers, though if you are following the book in a linear fashion, IIRC pointers are introduced later on.
Untested (namely for demonstrative purposes) code below.
NOTE: I took some liberties in reformatting your code for brevity.
#include <stdio.h>
#include <ctype.h>
#define TAB 8
#define MAXLINE 1000
int getmine(char s[], int lim);
int entab(char output[], int pos, int space);
int main()
{
char line[MAXLINE], output[MAXLINE];
int i;
while ((i = getmine(line, MAXLINE)) > 0) {
int space = 0;
int pos = 0;
int read_bytes = 0;
int write_bytes = 0;
while(read_bytes < i) {
if (line[read_bytes] != ' ') {
space = 0;
output[write_bytes++] = line[read_bytes];
}
else if (line[read_bytes] == ' ') {
space++;
if (line[read_bytes + 1] != ' ') {
if (space > TAB) {
write_bytes += entab(output, write_bytes, space);
} else {
for (int i = 0; i < space; i++)
output[write_bytes++] = ' ';
}
}
}
read_bytes++;
}
if (line[read_bytes] == '\n') {
output[write_bytes++] = line[read_bytes];
}
output[write_bytes] = '\0';
printf("%s", output);
}
}
int getmine(char s[],int lim)
{
int c, i;
for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
s[i] = c;
if (c == '\n') {
s[i] = c;
++i;
}
s[i] = '\0';
return i;
}
int entab(char output[], int pos, int space)
{
int nTabs = 0;
int nSpaces = 0;
int x = TAB - (pos % TAB);
if (x > 0) {
output[pos] = '\t';
space = space - x;
nTabs = space / TAB;
nSpaces = space % TAB;
for (int i = 0; i < nTabs; i++)
output[pos + 1 + i] = '\t';
for (int i = 0; i < nSpaces; i++)
output[pos + 1 + nTabs + i] = ' ';
return nTabs + nSpaces + 1;
} else if (x == 0) {
nTabs = space / TAB;
nSpaces = space % TAB;
for (int i = 0; i < nTabs; i++)
output[pos + i] = '\t';
for (int i = 0; i < nSpaces; i++)
output[pos + nTabs + i] = ' ';
}
return nTabs + nSpaces;
}

Answer 2

In my solution I used external variables for index counter of output line.
And I made separated function for converting input array to output array.
#include <stdio.h>
#define TAB 8
#define MAX 100;
int j; //counter of newline
char line[MAX];
char newline[MAX];
int getter(void);
void converter(void);
int entab(int space_counter, int line_index);
int main()
{
extern char line[];
extern char newline[];
int len;
while ((len = getter()) > 0) {
converter();
printf("%s", newline);
}
}
int getter()
{
int c;
int i;
i = 0;
while ((c = getchar()) != EOF && c != '\n' && i < 30-1) {
line[i] = c;
++i;
}
if (c == '\n') {
line[i] = c;
++i;
}
line[i] = '\0';
return i;
}
void converter(void)
{
extern int j;
extern char line[];
extern char newline[];
int space_counter;
int i;
i = j = 0;
space_counter = 0;
while (line[i] != '\0') {
while (line[i] == ' ') {
space_counter++;
i++;
}
if (space_counter > 0) {
j = entab(space_counter, i);
space_counter = 0;
}
else {
newline[j] = line[i];
j++;
i++;
}
}
newline[j] = '\0';
}
int entab(int space_counter, int end_point)
{
extern int j;
extern char newline[];
int new_index;
int start_point;
int tab_qty;
int space_qty;
start_point = end_point - space_counter;
tab_qty = end_point / TAB - start_point / TAB;
if (TAB > start_point)
space_qty = space_counter;
else
space_qty = end_point % TAB;
for (tab_qty; tab_qty > 0; tab_qty--) {
newline[j] = '\t';
j++;
}
for (space_qty; space_qty > 0; space_qty--) {
newline[j] = '|';
j++;
}
return new_index = j;
}