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I'm about to start work on a program that will sort strings in alphabetical/numerical order. I searched the tutorials and the FAQ, but I didn't see anything that would help with this. Could anybody give me some sample code to get me started on this? Thank you in advance.
just check the first element in the array and move then around that way...
Um... That's exactly what I don't know how to do. Can you post a snippet of code to get me started?
Code:for( int i = 0; i < numStrings; i++ )
{
for( int j = i; j < numStrings - 1; j++ )
{
if( strings[ j ] < strings[ j + 1 ] )
{
string temp = strings[ j ];
strings[ j ] = strings[ j + 1 ];
strings[ j + 1 ] = temp;
}
}
}
Thank you! Now I've gotta copy it onto my laptop... Ah well. Thanks again.
Edit: Sorry, maybe I'm just stupid. I can't figure out how that works. Could you possibly tell me how?
Nobody can help me out anymore? Guess I have to wait another 5 hours.
Well havn´t XSquared answered your question? XSquared uses a sort algorithm called bubble sort. Make a serach here or on The beloved google insteed of waiting.Quote:
Nobody can help me out anymore? Guess I have to wait another 5 hours.
I suggest a different solution. After all, this is the C++ forum, and what's the point of programming in C++ if you're not going to write some classes?
Write a string class. Overload the boolean operators for this class. Once you implement that, you can use any ole sort you please that makes use of the boolean operators. I love classes :)
Include the algorithm, string, and vector headers... then, put all the strings in the vector and use the following:
Code:#include <algorithm>
#include <string>
#include <vector>
int main(void)
{ std::vector< std::string > myList;
//populate myList with data
std::sort(myList.begin(), myList.end());
//myList is now sorted
}
If you want to use your own method of comparison instead of the default operator<, give the sort function a third parameter of your sorting function. For more info, check out here
Ok, I'm starting to get really confused...
Anyway, yesterday I found code for this in the source code section of this site (here). I copied that out, modified it to C++ commands and stuff, and it generated an error on the line:
My compiler tells me that there is a syntax error on that line, and that a ';' is missing before the '}'. Now, I can see that there's no right brace on that line, so is my compiler just messed up (Microsoft Visual C++ 6.0 Intro. Ed.)? Or is there something I'm missing?Code:SWAP(a[j-1],a[j]);
ive been seeing std in codes and stuff. and i know that it deals with strings but what else does it do and deal with? i dont really know what it is as for me getting confused and being a noob. seeing it in alot of peoples layout and dont know what they mean..
If your speaking of std like in this code:
it means you are creating a string object from the std (standard) namespace...After learning C++ basics I would suggest "The C++ Standard Library" by Nicolai M. Josuttis. I recently bought it and it has been great for a reference on the standard library, although I've been told its more of a standard template library reference.Code:#include <string>
int main(void)
{
std::string myStr("string");
}
alright thanks let me write that in my notebook :) so this should tell me about the standard librarys right? and is it easy to understand?Quote:
I would suggest "The C++ Standard Library" by Nicolai M. Josuttis.
Its not really that easy to understand so like I said make sure you have a good grasp on C++ before trying this book
Although many people would say its not a good book, I found "Sam's Teach Youself C++ in 21 Days" to be easy to understand and it included a variety of subjects
Edit: And as long as you get the most recent version it was also compliant with C++ standard AFAIK (uses the std namspace, etc.)
Ok... Now, could we get back on topic and answer my question? Thanks :)
The code from that link compiles fine for me...but can I see your modified code?Quote:
Anyway, yesterday I found code for this in the source code section of this site (here). I copied that out, modified it to C++ commands and stuff, and it generated an error on the line:
Ok, here it is:
Sorry for indentations, I program on my laptop but its not connected to the 'net, so I can't just copy and paste.Code:#include <iostream.h>
#include <stdio.h>
#include <stdlib.h>
#define SWAP(a,b) {int t; t=a; a=b; b=t}
#define INDEX 8
void bubble_srt(int a[], int n);
int main(void)
{
int i;
int array[INDEX] = {12, 8 35, 92, 19}; //Altered the numbers...
cout<<"Before sorting:"<< endl;
for(i=0; i<INDEX; i++)
cout<< array[i]<< endl;
bubble_srt(array, INDEX);
cout<<"After the sort:"<< endl;
for(i=0; i<INDEX; i++)
cout<< array[i]<< endl;
system("pause");
return 0;
}
void bubble_srt(int a[], int n)
{
int i, j;
for(i=0; i<n; i++)
{
for(j=1; j<(n-1); j++)
{
if(a[j-1]<a[j])
SWAP(a[j-1], a[j]);
}
}
}
You forgot a semicolon in your function and a comma in your array..also I don't really know the rules about macros since I haven't really used them, but adding another argument to use as a tmp worked...just pass the first value twiceCode:#include <iostream>
#include <cstdlib>
#define SWAP(a,b,c) { a=c; c=b; }
#define INDEX 8
using namespace std;
void bubble_srt(int a[], int n);
int main(void)
{
int array[INDEX] = {12, 8, 35, 92, 19}; //Altered the numbers...
cout<<"Before sorting:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
bubble_srt(array, INDEX);
cout<<"After the sort:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
system("pause");
return 0;
}
void bubble_srt(int a[], int n)
{
int i, j;
for(i=0; i<n; i++)
{
for(j=1; j<(n-1); j++)
{
if(a[j-1]<a[j]);
SWAP(a[j-1],a[j-1], a[j]);
}
}
}
Code:SWAP(val1,val1,val2);
Ok, thanks. I thought I may have just been missing something because I had to copy from one computer to another... Thanks. By the way, do you know of a way that I could make the values strings isntead of numbers?
Well making the values chars would be easy enough, but strings would be a bit difficult...for chars just make the array a char array instead of an integer array
And when you get tired of screwin around with that C stuff, give C++ a try:
Code:#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main( int argc, char** argv ) {
string test( "da1feb2c3a" );
sort( test.begin(), test.end() );
cout <<test <<endl;
}
Ok, thanks. It still gives me an error though. It says that 'std' doesn't exist or isn't a namespace.
Also, it said it couldn't use cstdlib.h, so I just removed that line.
Edit: Ok, I commented out the line 'using namespace std; and it got rid of all errors and warnings. I run the program, and for 'Before sorting:' it says 8. For 'After the sort:' it displays the following:
0
0
0
0
0
0
0
0
Now, maybe its just me, but that doesn't look like its working properly. Anybody have any idea what's going wrong?
Ok, I'm gonna bump this before it slips off the page... Can't anybody help me?
Post your exact source code.
Ok, sorry...
Code:#include <iostream.h>
#include <stdlib.h>
#include <stdio.h>
#define SWAP(a,b,c) { a=c; c=b; }
#define INDEX 8
//using namespace std;
void bubble_srt(int a[], int n);
int main(void)
{
int array[INDEX] = {12, 8, 35, 92, 19}; //Altered the numbers...
cout<<"Before sorting:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
bubble_srt(array, INDEX);
cout<<"After the sort:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
system("pause");
return 0;
}
void bubble_srt(int a[], int n)
{
int i, j;
for(i=0; i<n; i++)
{
for(j=1; j<(n-1); j++)
{
if(a[j-1]<a[j])
SWAP(a[j-1],a[j-1], a[j]);
}
}
}
Your swap is wrong. Macros are, well, evil. They expand in place, so your line where you call swap evaluates to:
Say a[j-1] is 33, a[j] is 4. Then, the first expression sets a[j] to 33. At this point both a[j] and a[j-1] are 33, so the next line does nothing -- that 4 is lost forever.Code:SWAP(a[j-1],a[j-1], a[j]);
||
\/
a[j] = a[j-1]; a[j-1] = a[j];
Also, a swap with three parameters is confusing.
Do this instead:
Your macro gains nothing by being a macro, and macros should be avoided whenever possible.Code:inline void swap(int &a, int &b){
int temp = a;
a = b;
b = temp;
}
Here is a more efficient way of swapping:
This uses the exclusive OR operation to swap the variables and does not require a temporary variableCode:inline void swap( int* a, int* b ) {
*a ^= *b;
*b ^= *a;
*a ^= *b;
}
Is that really more efficent, though? It still requires three passes through an ALU, and none of the operations can happen in parallel.
Ok, neither of those work, and I'm not even going to bother putting the errors up. Does anybody know a way to fix my code that will actually work?
Those swap methods both work just fine. The problems are in your code:
1) You have INDEX declared as 8 but have only 5 entries.
2) You use deprecated headers.
3) Your bubblesort isn't actually implementing the bubblesort algorithm.
Code://old headers
#include <iostream.h>
#include <stdlib.h>
#include <stdio.h>
Code://new headers
#include <iostream>
#include <cstdlib>
//use the std namespace
using namspace std;
I said cstdlib.h can't be used...
And Cat, if there were multiple problems, why did you only tell me of the one? I fixed the Index thing, and it says that before the sort it is "5" and after it is "8, 8, 35, 92, 19" instead of "8, 12, 19, 35, 92." Also, if both of those swap functions work fine, why do they both generate this error:
"'swap' : local function definitions are illegal?"
I only noticed the swap at first (which is a big problem).
The duplication is because the swap function is still broken.
They both DO work fine, but perhaps you put the function definition in the wrong place. This was my working code:
Code:#include <iostream>
#include <cstdlib>
#include <cstdio>
using namespace std;
inline void swap(int &a, int &b){
int temp = a;
a = b;
b = temp;
}
#define INDEX 5
void bubble_srt(int a[], int n);
int main(void)
{
int array[INDEX] = {12, 8, 35, 92, 19}; //Altered the numbers...
cout<<"Before sorting:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
bubble_srt(array, INDEX);
cout<<"After the sort:"<< endl;
for(int i=0; i<INDEX; i++)
cout<< array[i]<< endl;
}
void bubble_srt(int a[], int n)
{
int i, j;
for (i=0; i<n-2; i++) {
for (j=0; j<n-1-i; j++){
if (a[j+1] < a[j])
swap(a[j],a[j+1]);
}
}
}
Hey, that actually worked... Now I've gotta get it on my laptop @_@ Anyway, thanks.
Ok, I haven't copied that completely out onto my laptop, but for some reason cstdlib and cstdio aren't on there, but they're on this computer. So, I don't think that will work on it. I'll give it a try now, though. I'll let you know how it works (or doesn't :-P)
Just out of curiousity...why don't you just use the std::sort( ) function (from <algorithm>) to do this like I showed in a previous post?
Well, it's (very slightly) more memory efficient. I dunno, I just don't like decalring variables that I don't have to. I threw it in there because I thought it was kind of a cool tidbit...and I like being crafty with booleans. As far as speed effeciency, yeah there probably is no noticable difference, although I've never tested it.Quote:
Is that really more efficent, though? It still requires three passes through an ALU, and none of the operations can happen in parallel.
I will try it, I was just using the first one thrown at me to get it to work. And, hey, it did. Its interesting though... I dropped the .h from the end of cstdlib and cstdio and it worked. Now I just have to figure out how to get it to work with words. Thanks for all the help guys.
Standard C++ headers do not have .h on the end. If I wanted to use the C standard header stdlib.h, typically C++ headers drop the .h and add a 'c' to the front, thus <cstdlib>.
Indeed, none of the C++ standard headers include a .h; for example, #include <iostream> is standard, #include <iostream.h> is NOT standard, and not guaranteed to work.
Oh... There have been times where dropping the .h hasn't worked for me, so I tend to leave the .h there. Also, I've gotten the program to work for sorting numbers that the user types in, but sometimes when I use some 3 or 4 digit numbers it'll mess up. For example, I can put in 9, 7054, 7654, 745, and 5. The output will end up being:
9
5
745
7045
7654
Does anybody know why that might be? The code is the exact same as Cat's in his last post, with the exception of the addition of 5 new variables, a prompt to enter some numbers, and the numbers being replaced by the variables.
That's the C++ solution to your problem. If you don't know what vectors are or how to use them, I strongly suggest learning.Code:#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
vector<int> numbers;
int temp;
cout <<"Enter five numbers to sort: " <<endl;
for( int iter = 1; iter <= 5; iter++ ) {
cout <<"#" <<iter <<": ";
cin >>temp;
numbers.push_back( temp );
}
sort( numbers.begin(), numbers.end() );
cout <<"\nSorted list: " <<endl;
for( int index = 0; index < numbers.size(); index++ )
cout <<numbers[index] <<endl;
}