Strange behavior with counting spaces and tabs program

Question

C code

#include <stdio.h>

int main () 
{
    int c , nother , new , ndigits [10] , white, tabs ; 

    for ( int i = 0 ; i< 10 ; i++)
        ndigits[i] = 0 ;

    while ( (c = getchar() )!= EOF ) 
    {
        switch (c)
        {
            case '0' : case '1' : case '2' : 
            case '3' : case '4' : case '5' : 
            case '6' : case '7' :  case '8' : 
            case '9' : 
                ndigits[c- '0' ]++ ; 
                break ; 

            case ' '  : 
                printf("w");  /*to see how many spaces */
                white++ ; 

            case '\t' :
                printf("t");
                tabs++;

            case '\n' : 
                printf("n");
                new++ ; 
                break ; 

            default : 
                nother++ ; 
                break ;     
        }
    }

    printf ("digits = " ) ; 

    for ( int i = 0 ; i < 10 ; i++ ) 
        printf ("%d" , ndigits[i]) ;

    printf ( ",tabs = %d , new line = %d,  spaces = %d , other = %d ",
        tabs, white , new , nother ); 

    return 0 ;
}

When I compile it using GCC and just press Ctrl + z it prints

digits = 00000 , tabs = 4200912 , new line = 4194432 , spaces = 2293540 other = 2147307520

where these number come from ?
I compile it again and enter HELLO HELLO HELLO and click enter and it prints wtnwtnwnn
- why is that (there is 3 n than expected , why it counts three tabs ) ?

You initialized `ndigits[i]` to zero. What about `white`, `tab`, etc.? — Sergey Kalinichenko, Apr 22 '17 at 12:37
yes i forget to initialized other variables :) but I compile it again and enter HELLO HELLO HELLO and click enter and it prints wtnwtnwnn why is that (there is 3 n than expected , why it counts three tabs ) ? — Abdelrhman Fawzy, Apr 22 '17 at 12:42
Also missing `break`s? And you'll be less likely to make such mistakes with a sane coding style (indentation etc). Go read K&R! — John Hascall, Apr 22 '17 at 12:44

Paolo · Answer 1 · 2017-04-22T13:01:06.157

Initialize to zero the counters otherwise their initial value will be unpredictable.

int c , nother = 0 , new = 0 , ndigits [10] , white = 0, tabs = 0 ;

Also each case block (except the ones that catch digits) must be terminated with break; to achieve the expected result.

If you omit them the next instructions will be executed.

white++;
break;

...

tabs++;
break;

Bottom note: you would have found by yourself these mistakes by just enabling warnings on the compiler. Do it: you'll save a lot of time spotting naive errors.

Emil Laine · Accepted Answer · 2017-04-22T12:47:24.457

2

Some of your cases are missing breaks, which doesn't seem to be what you want.

Also you haven't initialized nother, new, white, and tabs, but are using them anyway. This results in undefined behavior. (Any decent compiler will give you a warning about this.)

edited Apr 22 '17 at 12:47

answered Apr 22 '17 at 12:41

Emil Laine

41,598
9
101
157

1

Indeed `case ' ':` will print `wtn`. – Weather Vane Apr 22 '17 at 12:46
I edited the above code.its given at the bottom.But it gives output as if expected – Mathews Sunny Apr 22 '17 at 13:14
@Downvoter: How is this or any of the other answers "not useful"? – Emil Laine Apr 22 '17 at 13:46
I'm not the downvoter, but I would have included a statement similar to: *when compiling, always enable all the warnings then fix those warnings (for `gcc`, at a minimum use: `-Wall -Wextra -pedantic` ) – user3629249 Apr 23 '17 at 19:27

Mathews Sunny · Answer 3 · 2017-04-22T13:06:12.400

There were several mistakes :

you were just declaring the variables and not initializing them.Thus a garbage value was inserted into those variables
It was printing 'n' errorneously as you haven't specified the break for the above statement.
You were printing no. of spaces as if number of lines ( check it printf (",tabs = %d , new line = %d, spaces = %d , other = %d " ,tabs ,white , new, nother) ; )

the following code generate the output you need :

    #include <stdio.h>

     int main () 
       {
    int c=0,nother=0,new=0,ndigits[10],white=0,tabs=0,i=0 ; 
    for ( i = 0 ; i< 10 ; i++)
        ndigits[i] = 0 ;
    while ( (c = getchar() )!= EOF ) 
    {
        switch (c)
        {
            case '0' :
            case '1' :
            case '2' : 
            case '3' :
            case '4' :
            case '5' : 
            case '6' :
            case '7' :
            case '8' : 
            case '9' : 
                      ndigits[c- '0' ]++ ; 
                      break ; 
            case ' '  : 
                       printf("w");  /*to see how many spaces */
                       white++ ; 
            case '\t' :
                       printf("t");
                       tabs++;
                       break;
            case '\n' : 
                           {
                        printf("n");
                        new++ ; 
                        break ; 
                             }
            default : 
                      nother++ ; 
                      break ;     
        }
    }
    printf ("digits = " ) ; 
    for (i = 0 ; i < 10 ; i++ ) 
        printf ("%d" , ndigits[i]) ;
    printf (",tabs = %d , new line = %d,  spaces = %d , other = %d " ,tabs , new,white , nother) ; 
    return 0 ;
      }

check it .it works well. – Mathews Sunny Apr 22 '17 at 13:07 — Mathews Sunny, Apr 22 '17 at 13:07

Strange behavior with counting spaces and tabs program

3 Answers3