Need help with K&Rc entab exersice

**karthy** · 12-01-2016

Code:

#include<stdio.h>

#define TAB 8 

int main()
{
    int tabs = 0, spaces = 0, pos = 1, c = 0;
    while((c = getchar()) != 0) {
        if(c == ' ') {
            ++spaces;
            if(spaces == 7) {
                ++tabs;
                spaces = 0;
            }
        } else {
            if((pos % TAB) - 1 == 0 && spaces > 0 && tabs == 0 ) {
                putchar('\t');
                spaces = spaces - (TAB- (pos-1 % TAB));
            }
            for(;0 < (spaces + tabs);) {
                if(tabs > 0) {    
                    putchar('\t');
                    --tabs;
                } else {
                    putchar('#');
                    --spaces;
                
                }

            }
            putchar(c);
            if(c == '\t')
                pos = pos + (TAB - (pos-1 % TAB) );
            else
                ++pos;
            if(c == '\n') 
                pos = 1;
        }
    }
    
    return 0;
}

Thats my code it doesn't work for long inputs i can't understand why how do i fix it.
this is k&Rc exersize 1-21 question

**Salem** · 12-01-2016

Did you start by sketching out on paper all the things you needed to do, or did you just hack together some code?

For example, do you know what the following should do (where <s> and <t> are space and tab respectively)?
hello
<s>hello
<s><s><s><s><t>hello
<t>hello

Try using a debugger to follow the actual program flow.
I typed in "<s><s>hello\n" and followed what happened.

Code:

$ gcc -Wall -g foo.c
$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) list
1	#include<stdio.h>
2	 
3	#define TAB 8 
4	 
5	int main()
6	{
7	    int tabs = 0, spaces = 0, pos = 1, c = 0;
8	    while((c = getchar()) != 0) {
9	        if(c == ' ') {
10	            ++spaces;
(gdb) b 9
Breakpoint 1 at 0x40059f: file foo.c, line 9.
(gdb) run
Starting program: /home/sc/Documents/a.out 
  hello

Breakpoint 1, main () at foo.c:9
9	        if(c == ' ') {
(gdb) print c
$1 = 32
(gdb) n
10	            ++spaces;
(gdb) 
11	            if(spaces == 7) {
(gdb) 
8	    while((c = getchar()) != 0) {
(gdb) 

Breakpoint 1, main () at foo.c:9
9	        if(c == ' ') {
(gdb) 
10	            ++spaces;
(gdb) 
11	            if(spaces == 7) {
(gdb) 
8	    while((c = getchar()) != 0) {
(gdb) 

Breakpoint 1, main () at foo.c:9
9	        if(c == ' ') {
(gdb) print (char)c
$3 = 104 'h'
(gdb) n
16	            if((pos % TAB) - 1 == 0 && spaces > 0 && tabs == 0 ) {
(gdb) print pos
$4 = 1
(gdb) n
17	                putchar('\t');
(gdb)

What is pos actually supposed to mean?
You're only supposed to be outputting two spaces in this instance.

Finally, your while loop should read

Code:

while((c = getchar()) != EOF)

**karthy** · 12-01-2016

pos is the position of the imaginary pointer. It prints # for spaces btw, It works if i replace \t in the program to 8 spaces lol I think evey time there is a tab and there is a tabstop before 7 spaces it gets offset by some spaces, I want it to print tab and then fill the rest with # because a tab is not exactly 8 spaces and i assumed that was the case when i wrote this code.

If I replace \t in the program by 8 spaces it works fine
here's tab = 7 spaces code

Code:

#include<stdio.h>

#define TAB 8 

int main()
{
    int tabs = 0, spaces = 0, pos = 1, c = 0, sync = 0;
    while((c = getchar()) != EOF) {
        if(c == ' ') {
            ++spaces;
            if(spaces == 7) {
                ++tabs;
                spaces = 0;
            }
        } else {
            if((pos % TAB) - 1 == 0 && spaces > 0 && tabs == 0 ) {
                printf("       ");
                spaces = spaces - (TAB- (pos-1 % TAB));
            }
            for(;0 < (spaces + tabs);) {
                if(tabs > 0) {
                sync += (TAB -(pos-1 % TAB));    
                    printf("       ");
                    --tabs;
                } else {
                    putchar('#');
                    --spaces;
                
                }

            }
            putchar(c);
            if(c == '\t')
                pos = pos + (TAB - (pos-1 % TAB) );
            else
                ++pos;
            if(c == '\n') 
                pos = 1;
        }
    }
    
    return 0;
}

how to i make it so that if it tabstop's early it will fill the rest with #

**algorism** · 12-01-2016

This is just a while loop:

Code:

            for ( ; 0 < (spaces + tabs); ) {

It's also written backwards (are you arabic?) and has extraneous parens:

Code:

            while (spaces + tabs > 0)

This

Code:

            if (spaces == 7) {

should be

Code:

            if (spaces == TAB - 1) {

The following needs to be a loop so it will handle different TAB sizes.

Code:

                printf("       ");

Can you see anything wrong with the following? Missing parens perhaps?

Code:

    (pos - 1 % TAB)

The tabsize should be a command line parameter.

Code:

#define DEFAULT_TABSIZE 8

int main(int argc, char **argv) {
    int tabsize = DEFAULT_TABSIZE;
    if (argc > 2) { } // error: bad parameters
    if (argc == 2) tabsize = atoi(argv[1]);
    if (tabsize < 1) { } // error: insane tabsize

You should put spaces after your 'if', 'while', 'for', keywords (and 'include', for that matter). That's what most people do (they're not function calls).

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