Question

When trying to compile the following code, I am getting a warning that line 18 makes integer from pointer without cast and that 19 and 20 are incompatible types in assignment. I am new to structures in C, and can’t seem to figure out what is wrong.

#include <stdio.h>

struct song
{       char title[70];
};

struct playlist
{       struct song songs[100];
};

void title_sort(struct playlist * list,int len)
{       int swapped = 1,i;
        char hold;
        while (swapped)
        {       swapped = 0;
                for (i = 0;i < len - 1; i++)
                {       if (list->songs[i].title > list->songs[i+1].title)
                        {       hold = list->songs[i].title;
                                list->songs[i].title = list->songs[i+1].title;
                                list->songs[i+1].title = hold;
                                swapped = 1;
                        }
                }
        }
}

int main()
{       struct playlist playlist;
        int i;
        for (i = 0;i < 5;i++)
        {       fgets(playlist.songs[i].title,70,stdin);
        }
        title_sort(&playlist,5);
        printf("\n");
        for (i = 0;i < 5;i++)
        {       printf("%s",playlist.songs[i].title);
        }
        return 0;
}

Answer 1

You can’t compare strings in C with >. You need to use strcmp. Also hold is char but title is char [70]. You could copy pointers to strings but arrays can’t be copied with just =.

You could use strcpy like this:

void title_sort(struct playlist * list,int len)
{       int swapped = 1,i;
        char hold[70];
        while (swapped)
        {       swapped = 0;
                for (i = 0;i < len - 1; i++)
                    {       if (strcmp (list->songs[i].title, list->songs[i+1].title) > 0)
                            {       strcpy (hold, list->songs[i].title);
                                strcpy (list->songs[i].title, list->songs[i+1].title);
                                strcpy (list->songs[i+1].title,hold);
                                swapped = 1;
                        }
                }
        }
}

But please note that in C you need to check things like the lengths of strings, so the above code is dangerous. You need to either use strncpy or use strlen to check the lengths of the strings.