do while loop

DJMK4 · 6 Mar 2006 at 12:09

Code:

do { pass = 1; pass<=arraysize-1; pass++;

	}


    while (swap == false);

I need abit of help with some c++, how would i say do the following while swap == false?

it needs to sort through an array of data whilst swap is equal to false, once everything is swapped bool swap will change to true and the programme will exit..

I have the rest of the code i just not sure what to put in this first do while loop.

Cold_And_Miserable · 6 Mar 2006 at 12:25

do
{
for(pass= 1;pass<=arraysize-1;pass++)
{
COMMAND HERE;
}
}while(swap == false);

Visage · 6 Mar 2006 at 13:20

If you're just looking to sort a load of data (i'm guessing here, from looking at what you've posted), why not just use the standard sort algorithms?

Dfhaii · 6 Mar 2006 at 13:33

The loops uses a boolean condition so you don't need while (swap == false), you can use while (!swap) instead.

DJMK4 · 6 Mar 2006 at 19:33

Dfhaii said:
The loops uses a boolean condition so you don't need while (swap == false), you can use while (!swap) instead.

Thats the way iv been shown how to do it im afaid, here is my code

Code:

#include <iostream.h>
#include <cstring.h>

void main()

{

//Variable declarations
int item[10];
int pass;
int comparison;
int temp;
int arraysize;
int i;
bool swap;

//input

item[0] = 2;
item[1] = 1;
item[2] = 3;
item[3] = 4;
item[4] = 7;
item[5] = 5;
item[6] = 9;
item[7] = 6;
item[8] = 8;
item[9] = 10;

arraysize = 10;

//sorting

pass = 1;
do {

	for (comparison=1; comparison <= arraysize-1; comparison++)
      {

        	if (item[comparison-1] > item[comparison])
         {
         swap = true;


         temp = item[comparison-1];
         item[comparison-1] = item[comparison];
         item[comparison] = temp;

			}



		}

    pass++;
    while ((swap == false) && (pass<=arraysize-1));






	}
//output



cout<<""<<endl;
cout<<""<<endl;
cout<<"State of array after sorting: "<<endl;

for (i = 0;  i<10; i++)
{
cout<<item[i]<<endl;


}






}

Im trying to find a place for that pass++, am i correct in saying that it goes somewhere before the while loop, because i only want to increment further if swap == true, if there are no swaps (swap== false) then there is no-need to increment any further and the loop will finish.

I want to try to keep with the structure im working with, any one telling me i shouldnt do this, replace this with this as it will only confuse me more.

robmiller · 6 Mar 2006 at 20:09

if and while just evaluate the contents of the parentheses and see if they're true, so it's usually just as readable and much easier to negate the variable with !:

Code:

// in C++...
if(foo == false)
if(foo == 0)
if(!foo)
// ...are equivalent

DJMK4 · 6 Mar 2006 at 23:05

robmiller said:
if and while just evaluate the contents of the parentheses and see if they're true, so it's usually just as readable and much easier to negate the variable with !:

Code:

// in C++... if(foo == false) if(foo == 0) if(!foo) // ...are equivalent

I dont get what you mean?

You mean replacing (statement == false) with (!statement)

Lagz · 7 Mar 2006 at 00:13

Yes he is just saying they are the same. Just use the method you have been taught (foo == false) it its more natural/readable for you. The other way (!foo) is just a bit shorter. Dont use (foo==0) . . its a bit confusing.

Swanster · 7 Mar 2006 at 00:14

Essentially, to get the code working you're going to need to change:

Code:

}

    pass++;
    while ((swap == false) && (pass<=arraysize-1));

}
//output

to

Code:

		}
        pass++;
   } while ( (swap == false) && (pass<=arraysize-1) );

However, instead of "while ((swap == false) && (pass<=arraysize-1));", you could also write
"while ( !swap && (pass<=arraysize-1) );" - both do exactly the same.

Btw, what are you using to compile this? as I had to change the top of the file to:

Code:

#include <iostream>
#include <stdlib.h>

using namespace std;

int main()

to get it to compile.

DJMK4 · 7 Mar 2006 at 00:24

Swanster said:
Essentially, to get the code working you're going to need to change:

Code:

} pass++; while ((swap == false) && (pass<=arraysize-1)); } //output

to

Code:

} pass++; } while ( (swap == false) && (pass<=arraysize-1) );

However, instead of "while ((swap == false) && (pass<=arraysize-1));", you could also write
"while ( !swap && (pass<=arraysize-1) );" - both do exactly the same.

Btw, what are you using to compile this? as I had to change the top of the file to:

Code:

#include <iostream> #include <stdlib.h> using namespace std; int main()

to get it to compile.

Thanks a lot mate, that makes more sence to me..Ill probably do it one way then add the alternative as a comment

Well we use a version of Borland C++ 5.02 i think, but i use bloodshed dev C++ at home

DJMK4 · 7 Mar 2006 at 00:48

Why aint in compiling in bloodshed dev C++??

its complaning about the bits of code like cout<<""<<endl; which worked fine on borlands version of C++..

I have created a new project and put the code in

here is my code

Code:

#include <cstdlib>
#include <iostream>
#include <cstring>
#include <istream>
using namespace std;

int main(int argc, char *argv[])
{

    //Variable declarations
int item[10];
int pass;
int comparison;
int temp;
int arraysize;
int i;
bool swap;

//input

item[0] = 2;
item[1] = 1;
item[2] = 16;
item[3] = 4;
item[4] = 7;
item[5] = 5;
item[6] = 9;
item[7] = 6;
item[8] = 8;
item[9] = 15;

arraysize = 10;

//sorting

pass = 1;
do {

	for (comparison=1; comparison <= arraysize-1; comparison++)
      {

        	if (item[comparison-1] > item[comparison])
         {
         swap = true;


         temp = item[comparison-1];
         item[comparison-1] = item[comparison];
         item[comparison] = temp;

			}



		}

    pass++;
   } while ( (swap == false) && (pass<=arraysize-1) );





	}
//output





cout<<" "<<endl;
cout<<"State of array after sorting: "<<endl;
for (i = 0;  i<10; i++)
{
cout<<item[i];<<endl;


}






}

    
    
    system("PAUSE");
    return EXIT_SUCCESS;
}

Swanster · 7 Mar 2006 at 10:29

The error is not the cout line, but above it.
You need to remove the '{' just above '//output', and the one just above 'system("PAUSE");'. You also need to take the ';' out of 'cout<<item;<<endl'.

DJMK4 · 7 Mar 2006 at 11:27

thanks

Una · 7 Mar 2006 at 11:33

Edit: nevermind someone else answered

DJMK4 · 7 Mar 2006 at 11:46

Iv noticed tho it does not sort my array items correctly

Code:

#include <iostream>
#include <stdlib.h>

using namespace std;

int main()
{

//Variable declarations
int item[10];
int pass;
int comparison;
int temp;
int arraysize;
int i;
bool swap;

//input

item[0] = 2;
item[1] = 1;
item[2] = 16;
item[3] = 4;
item[4] = 7;
item[5] = 5;
item[6] = 9;
item[7] = 6;
item[8] = 8;
item[9] = 15;

arraysize = 10;

//sorting

pass = 1;
do {

	for (comparison=1; comparison <= arraysize-1; comparison++)
      {

        	if (item[comparison-1] > item[comparison])
         {
         swap = true;


         temp = item[comparison-1];
         item[comparison-1] = item[comparison];
         item[comparison] = temp;

			}



		}

    pass++;
   } while ( (swap == false) && (pass<=arraysize-1) );





	
//output



cout<<""<<endl;
cout<<"State of array after sorting: "<<endl;

for (i = 0;  i<10; i++)
{
cout<<item[i]<<endl;






}
 system("PAUSE");
    return EXIT_SUCCESS;



}

Visage · 7 Mar 2006 at 13:17

Code:

#include <iostream>
#include <cstdlib>
#include <algorithm>

using namespace std;

int main()
{

//Variable declarations
int item[10];

//input

item[0] = 2;
item[1] = 1;
item[2] = 16;
item[3] = 4;
item[4] = 7;
item[5] = 5;
item[6] = 9;
item[7] = 6;
item[8] = 8;
item[9] = 15;

int arraysize = 10;

//sorting

std::sort(item, item+arraysize) ;
	
//output
cout<<""<<endl;
cout<<"State of array after sorting: "<<endl;

for (int i = 0;  i<arraysize; i++)
{
cout<<item[i]<<endl;
}

 system("PAUSE");
    return EXIT_SUCCESS;
}

ByteJuggler · 7 Mar 2006 at 14:11

[Sniper][Wolf] said:
Iv noticed tho it does not sort my array items correctly

I take it you're trying to implement bubble sort yourself. In that case your loop logic should be "keep repeating doing a pass while a swapped in the last pass", not while "not swapped" as you had it. When you've done a pass without swapping, then you're done (since all pairs of elements are in the correct order.)

Fixed code:

Code:

#include <iostream>
#include <stdlib.h>

using namespace std;

int main()
{
	//Variable declarations
	int item[10];
	int pass;
	int comparison;
	int temp;
	int arraysize;
	int i;
	bool swap;

	//input
	item[0] = 2;
	item[1] = 1;
	item[2] = 16;
	item[3] = 4;
	item[4] = 7;
	item[5] = 5;
	item[6] = 9;
	item[7] = 6;
	item[8] = 8;
	item[9] = 15;

	arraysize = 10;

	//sorting
	pass = 1;

	do {
		// start the pass remembering that we've not swapped yet:
		swap = false;

		// loop over the array, if we swap, set swapped to true
		for (comparison=1; comparison <= arraysize-1; comparison++)
		{
			if (item[comparison-1] > item[comparison])
			{
				swap = true;
				temp = item[comparison-1];
				item[comparison-1] = item[comparison];
				item[comparison] = temp;
			}
		}
		// incremement the pass count at the end of the pass
		pass++;
		// if we've swapped, then we must do another pass (since there might
		// still be unsorted entries.  (If swap == false we're done.)
	} while ( (swap == true) && (pass<=arraysize-1) );

	//output
	cout<<""<<endl;
	cout<<"State of array after sorting: "<<endl;

	for (i = 0;  i<10; i++)
	{
		cout<<item[i]<<endl;
	}

	system("PAUSE");
	return EXIT_SUCCESS;
}

HTH