Sorting case sensitive array not working in C

Question

I'm trying to sort a case sensitive array of words words[number of words][number of letters] alphabetically by strcmp using case insensitive array with same words. When I sort case insensitive array using case insensitive array and print it, it works, but if I try to sort case sensitive array using case insensitive array - it does not. Below are the blocks of code I am using to do this.


char cs_sns[20][20];
///scan here as you wish/////
char cs_ins[20][20];

for(int i = 0; i < 20; i++)
{
    strcpy(cs_ins[i], cs_sns[i]);
}

//////////////////CONVERT///////////////////////////
for(int i = 0; i < 20; i++)
{
    strlwr(cs_ins[i]);
}

 /////////////////SORT_CASE_SENSITIVE_BY_LOWERCASE/////////////////////


    for (int j = 0; j < 20; j++)
    {
        for (int i = 0; i < 20-1; i++)
        {
            int x = (strcmp(cs_ins[i], cs_ins[i+1]) > 0); 
            if (x == 1)
            {
                char temp[20];
                strcpy(temp, cs_sns[i]);
                strcpy(cs_sns[i], cs_sns[i+1]);
                strcpy(cs_sns[i+1], temp);
            }
        }
    }

/////////////////////SORT_LOWERCASE_BY_LOWERCASE/////////////////
    for (int j = 0; j < 20; j++)
    {
        for (int i = 0; i < 20 - 1; i++)
        {
            int x = (strcmp(cs_ins[i], cs_ins[i+1]) > 0); 
            if (x == 1)
            {
                char temp[20];
                strcpy(temp, cs_ins[i]);
                strcpy(cs_ins[i], cs_ins[i+1]);
                strcpy(cs_ins[i+1], temp);
            }
        }
    }

    ///////////////PRINT/////////////////

    for (int i = 0; i < 20; i++)
    {
        printf("%s\n", cs_sns[i]);       //////////swap with cs_ins[i] and see what happens
    }

Below is the stolen function strlwr to convert to lowercase.

///////////define strlwr/////////////////////

char *strlwr(char *str)
{
    unsigned char *p = (unsigned char *)str;

    while (*p) 
    {
        *p = tolower((unsigned char)*p);
        p++;
    }

    return str;
}

You'll need to include ctype.h for tolower.

What is it that I am missing? Thank you.

Edit: Can be solved by stricmp, here is a link: C99 remove stricmp() and strnicmp()?

Still curious tho...

Are you aware of `stricmp` function ? It does a case-insensitive comparison. — Youssef13, Dec 14 '19 at 15:58
You're using a variable `pos` - where is this defined and what is it set to? — Graeme Cole, Dec 14 '19 at 16:04
You don't have to copy entire strings on a swap. Just swap the pointers in the array. — lurker, Dec 14 '19 at 16:04
Oh, thank you, it works! It is not a part of C99 anymore, but there is a way to write it, i'll post a link. Still curious why this one is not working tho, it makes sense for me... — Pierre Rigondeaux, Dec 14 '19 at 16:05
@GraemeCole i forgot to swap it with the number 20, it is the amount of words. — Pierre Rigondeaux, Dec 14 '19 at 16:06
Also your first sorting loop is comparing the elements of `cs_ins` but swapping the elements of `cs_sns`. — Graeme Cole, Dec 14 '19 at 16:09
@chux-ReinstateMonica oh, i don't know, that is up to you, it should be max 19 characters long though, the 20th is for the null character. — Pierre Rigondeaux, Dec 14 '19 at 16:09
@GraemeCole That is the point, the order should be the same, if you strcmp compares ASCII values and ```a != A ```in that case. — Pierre Rigondeaux, Dec 14 '19 at 16:10
PierreRigondeaux, Tip: avoid `[20][20]`. Instead use something like `#define WORDS 20 #define SIZE` and then use those as in `ss_sns[WORDS][SIZE];` The re-use of 20 for the 2 dimension reduces clarity. — chux - Reinstate Monica, Dec 14 '19 at 16:13
@chux-ReinstateMonica Will do next time, the reality is that this is like a 1/15 of a code which involves dynamic allocation and pointer nightmares, since I am a beginner, so I tried to simplify it with numbers. Thank you and everybody for the help! — Pierre Rigondeaux, Dec 14 '19 at 16:15
Pierre Rigondeaux Good idea for simplifying. Still could have used numbers, but 2 different numbers makes for a clearer example. — chux - Reinstate Monica, Dec 14 '19 at 16:18

score 2 · Accepted Answer · answered Dec 14 '19 at 16:09

The problem occurs because you are trying to sort your case-sensitive array according to the case-insensitive array, while NOT CHANGING the insensitive array.

This may work:

 /////////////////SORT_CASE_SENSITIVE_BY_LOWERCASE/////////////////////


for (int j = 0; j < 20; j++)
{
    for (int i = 0; i < 20-1; i++)
    {
        int x = (strcmp(cs_ins[i], cs_ins[i+1]) > 0); 
        if (x == 1)
        {
            char temp[20];
            strcpy(temp, cs_sns[i]);
            strcpy(cs_sns[i], cs_sns[i+1]);
            strcpy(cs_sns[i+1], temp);
            //swap elements in cs_ins[] as well
            strcpy(temp, cs_ins[i]);
            strcpy(cs_ins[i], cs_ins[i+1]);
            strcpy(cs_ins[i+1], temp);
        }
    }
}

Thus applying the changes to the insensitive array as well.

Of course, just using stricmp would be a much simpler solution, as Monica has stated.

On POSIX systems, `stricmp()` is not necessarily available (it isn't part of the POSIX standard), but [`strcasecmp()`](http://pubs.opengroup.org/onlinepubs/9699919799/functions/strcasecmp.html) found in [``](http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/strings.h.html) is the alternative. Of course, `strlwr()` is not a POSIX function either. — Jonathan Leffler, Dec 14 '19 at 17:08

Sorting case sensitive array not working in C

1 Answers1