comparison is always true/false

jubaitca · 11-04-2006, 09:30 PM

Ok after trying to fix the errors, but I still get some errors. I think something is wrong when i am passing in the value.

Here is my new code:

Code:

void SelectionSort(char arr[][MAX_WORD_LENGTH+1], const int size)
{
	int smallest_index;

	for (int i= 0; i <=size; i++)
	{
		smallest_index = i;
		
		for (int j = i + 1; j <= size; j++)
		{
			if (strcmp(arr[j],arr[smallest_index]) < 0)
			{
			 	smallest_index=j;
			}
		
		}
		swap(arr[i],arr[smallest_index]);
	}			
}

void swap_words(char arr1[],char arr2[])
{
	char temp[strlen(arr1)];
	strncpy(temp,arr1,strlen(arr1));
	strncpy(arr1,arr2,strlen(arr2));
	strncpy(arr2,temp,strlen(temp));
}

Here is new set of error:
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algobase.h: In function `
void std::swap(_Tp&, _Tp&) [with _Tp = char[26]]':
test.c:73: instantiated from here
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algobase.h:130: error: in
valid initializer
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algobase.h:131: error: IS
O C++ forbids assignment of arrays
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_algobase.h:132: error: IS
O C++ forbids assignment of arrays

tuxdev · 11-04-2006, 09:38 PM

swap != swap words. Also, if swap_words is supposed to be local to that file only, put it in an anonymous namespace like

Code:

namespace // no name, anonymous
{
   // stuff
}

Also, if your code is assuming something (like the words really being the right size) then assert() it, after #include <cassert>

jubaitca · 11-04-2006, 09:52 PM

oh my god, I can be really stupid at times. Thanks very much though.

dogpatch · 11-04-2006, 09:57 PM

Quote:

if you can please give me a hand with my algorithm (my basic approach to do it). Is there something wrong with it?

As a basic approach, i would suggest you take one step at a time, instead of trying to code the entire program at once.

1.Code functions as stubs that do nothing but accept the arguments.
2.Understand and correct compile errors one at a time.
3.When you get a clean compile, finish coding each function one at a time.
4.When you finally have a clean compile, and the program doesn't work right, post a thread with the specifics of what's going wrong.

jubaitca · 11-05-2006, 10:45 AM

Thanks for the advice. I am error free now. But, now I run into a bigger problem. My output is not quite right.

My code now is the following:

Code:

void SelectionSort(char arr[][MAX_WORD_LENGTH+1], const int size)
{
	int smallest_index;

	for (int i= 0; i <=size; i++)
	{
		smallest_index = i;
		
		for (int j = i + 1; j <= size; j++)
		{
			if
				(strncmp(arr[j],arr[smallest_index],strlen(arr[smallest_index])) < 0)
			{
			 	smallest_index=j;
			}

		}
		swap_words(arr[i],arr[smallest_index]);
	}			
}

void swap_words(char arr1[],char arr2[])
{
	char temp[strlen(arr1)];
	strncpy(temp,arr1,strlen(arr1));
	strncpy(arr1,arr2,strlen(arr2));
	strncpy(arr2,temp,strlen(temp));
}

And my output is:

Quote:

the
war
of
the
worlds
by
h
g
-ells
-ook
-ne
-he
-oming
-f
-he
-artians
10,000,000
140,000,000
1894
2ve
35,000,000
ahe
aar
aut
aho
ahall
awell
an
ahese
aorlds
af
ahey
ae
anhabited
aheÿd◄A
aarÿd◄A
afrÿd◄A
are
ae
ar
ahey
aords
af
ahe
aorld
aheÿd◄A
aorldsA
ayrld◄A
and
aow
are
all
ahings
aade
aor
aan
aells◄A
aepler
auoted
an
ahe
anatomy
af
aelancholy
ao
ane
aould
aave
aelieved
about
about
about
about
about
about
abouteenth
aboutry
about
abundance
accelerated
across
across
acrossd
across
activity
adjacent
admits
advancegences
affairs
after
after
after
after
after
againl
against
against
against
agot
air
air

I think its repeating a lot of words, and some words aren't even being alphabetized. For example, the words in the begenning(they are in the begenning of the text file as well) aren't being sorted for some reason. And I think a lot of junk words are put in as well.

Is there anyhting wrong with my code?

dogpatch · 11-05-2006, 06:55 PM

Is the const variable 'size' what it appears to be, the size of the array? If so, your for loop stop condition should be using '<', not '<=' to quit the loop at the end of the array.

Secondly, your use of strncpy() on variable length words may be having unintended results. strncpy() will move 'n' characters from one string to the other. By moving only strlen(source_string) number of characters, you are not moving the null terminator to the destination string, which means the destination string may end up being longer than the source. Try

Code:

strncpy(strlen(source_string) + 1)

so that you are always moving the null byte, too.