reversing number

[yat89]

Hi everyone. I got a task to reverse number from index 2 to 5 for each row. I had try with the code but the solution wont appear. I dont know either i do right or wrong. Hope someone can help me. Thank you.

Input file:
1 2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8 9 10 1
3 4 5 6 7 8 9 10 1 2
6 5 4 3 2 1 7 8 9 10
5 7 9 1 3 4 6 10 2 8

 #include "stdafx.h"
#include <iostream> 
#include <algorithm> 
#include <vector> 
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <ctime>

using namespace std; 

const int n = 10;
const int m = 5;
vector< vector <int>> route (m, vector <int> (n,0));
  
int main() 
{ 
    ifstream inpData("myData.txt");

	//assign route into array                    
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			//cout << "route [" << i << "][" << j << "] = " << route[i][j] << endl;
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	//close input files
	inpData.close();

	for (int row = 0; row < m; row++)
	{
		cout << "Reverse only from index 2 to 5 for each row:\n"; 
		// Reversing elements from index 2 to index 5 
		reverse(route.begin() + route[row][2], route.begin() + route[row][5]); 
	}
	cout << endl;

	// Displaying solution
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	system("pause");
 
}

The output should be:
1 2 6 5 4 3 7 8 9 10
2 3 7 6 5 4 8 9 10 1
3 4 8 7 6 5 9 10 1 2
6 5 1 2 3 4 7 8 9 10
5 7 4 3 1 9 6 10 2 8

[nuderobmonkey]

Replace line 40 by:
reverse(route[row].begin() + 2, route[row].begin() + 5);
Don't hesitate to ask if its meaning is unclear to you.

[yat89]

Hi nuderobmonkey, i got it. Thanks for your help :)

[nuderobmonkey]

Oh, I see that I made a mistake. Line 40 should rather be:
reverse(route[row].begin() + 2, route[row].begin() + 6);
Because the last iterator needs to be one beyond the last element to reverse.

[yat89]

Thanks nuderobmonkey. If you don't mind. I would like to ask another question also regards to reverse. I had try with the code but its weird. sometimes i could get the answer but when i run for another time error occurred. If not be mistaken, I think it related to

srand(time(null))

. Because when I disable

srand(time(null))

. I could get the answer but when I include those, error occurred. I don't know how to solved it.

#include "stdafx.h"
#include <iostream> 
#include <algorithm> 
#include <vector> 
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <ctime>

using namespace std; 

const int n = 10;
const int m = 5;
vector< vector <int>> route (m, vector <int> (n,0));
  
int main() 
{ 
	//srand(time(null));
	//srand((unsigned int)time(NULL));

    ifstream inpData("myData.txt");

	//assign route into array                    
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			//cout << "route [" << i << "][" << j << "] = " << route[i][j] << endl;
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	//close input files
	inpData.close();

	for (int row = 0; row < m; row++)
	{

		// Generate two different random value from col to col + 14, inclusive.
        int i1, i2;
        do
        {
            i1 = rand() % 10;
            i2 = rand() % 10;
        }
        while (i1 == i2);

        // Ensure i1 is less than i2; if not, swap them.
        if (i1 > i2)
        {
            int temp = i1;
            i1 = i2;
            i2 = temp;
        }
        
        cout << "For row " << row << ", positions " << i1 << " and " << i2 << " were chosen.\n";

		// ============= Reverse & Swap ============"; 

		// Reversing elements from index (i1 + 2) to index (i2 - 1) 
		reverse(route[row].begin() + (i1 + 2), route[row].begin() + i2); 

		// Swap next value at position i1 with value at position i2.
		swap(route[row][i1 + 1], route[row][i2]);
	}
	cout << endl;

	// Displaying solution
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	system("pause");
 
}

[nuderobmonkey]

Could you describe precisely what error you get?

What are the values of i1 and i2, and what output do you get vs. what do you expect?

[yat89]

Could you describe precisely what error you get?

Debug assertion failed.
Expression: invalid iterator range.

What are the values of i1 and i2

i1 and i2 are two different random value positions from col 0 until col 9 for each row.

After i got two different random value, I do reverse number from index (i1 + 2) to index (i2 - 1) for each row.

After i reverse, I do swap next value at position i1 which is (i1 + 1) with value at position i2.

what output do you get

If I included srand(time(null)), the solution won't appear.
If I disable srand(time(null)), the solution appear but the random value is same for each run.

what do you expect?

Input:
1 2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8 9 10 1
3 4 5 6 7 8 9 10 1 2
6 5 4 3 2 1 7 8 9 10
5 7 9 1 3 4 6 10 2 8

For example, for row 0, position 1 and 8 were chosen.
i1 = position 1
i2 = position 8

1 2 3 4 5 6 7 8 9 10

The output should be
1 2 9 8 7 6 5 4 3 10

Hope you understand what i'm trying to explain.

[nuderobmonkey]

Oh, that's weird. When I compile and run your program at my, I get the correct output:

//#include "stdafx.h"
#include <iostream> 
#include <algorithm> 
#include <vector> 
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <ctime>

using namespace std; 

const int n = 10;
const int m = 1;
vector< vector <int>> route (m, vector <int> (n,0));
  
int main() 
{ 
	srand(time(nullptr));
	//srand((unsigned int)time(NULL));

    ifstream inpData("myData.txt");

	//assign route into array                    
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			//cout << "route [" << i << "][" << j << "] = " << route[i][j] << endl;
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	//close input files
	inpData.close();

	for (int row = 0; row < m; row++)
	{

		// Generate two different random value from col to col + 14, inclusive.
        int i1, i2;
        do
        {
            i1 = 1; //rand() % 10;
            i2 = 8; //rand() % 10;
        }
        while (i1 == i2);

        // Ensure i1 is less than i2; if not, swap them.
        if (i1 > i2)
        {
            int temp = i1;
            i1 = i2;
            i2 = temp;
        }
        
        cout << "For row " << row << ", positions " << i1 << " and " << i2 << " were chosen.\n";

		// ============= Reverse & Swap ============"; 

		// Reversing elements from index (i1 + 2) to index (i2 - 1) 
		reverse(route[row].begin() + (i1 + 2), route[row].begin() + i2); 

		// Swap next value at position i1 with value at position i2.
		swap(route[row][i1 + 1], route[row][i2]);
	}
	cout << endl;

	// Displaying solution
	for (int i = 0; i < m; i++ )
	{
		for (int j = 0; j < n; j++)
		{
			inpData >> route[i][j];
			cout << setw(3) << route[i][j] << ' ';
		}
		cout << endl;
	}
	cout << endl;

	//system("pause");
 
}

I made some changes because I need it to run on an unixoid os.

[yat89]

I had copy your changes and I try run. One error occurred.

error C2065: 'nullptr' : undeclared identifier

Actually, what is srand(time(nullptr)) ?

It is same with srand(time(null))

[nuderobmonkey]

What compiler (and version) do you use?

nullptr is a void pointer to address 0 and is builtin keyword since C++11. You could replace this by NULL or 0.

I suggest reposting your program in the 'Windows Program' forum if the error still will resist.

[yat89]

What compiler (and version) do you use?

I'm using Visual Studio 2008.

I had replace with NULL but error still occurred as previous.
and
warning C4244: 'argument' : conversion from 'time_t' to 'unsigned int', possible loss of data

I suggest reposting your program in the 'Windows Program' forum if the error still will resist.

Okay i will post. Btw, thanks for your help. Really appreciated :)

[jonnin]

null is defined in cstdlib among other places. check your includes, here is a link that may help..
It is often mistaken as a keyword, but its not really, its just a #define in that era of C++ at least...

https://en.cppreference.com/w/cpp/types/NULL

nullptr actually IS a keyword, but you don't have it, seeing as how your compiler is almost old enough to attend middle school...

I mean I see that you have cstdlib, and it should be in there... zero will work, if you can't find the issue, but a new compiler would do you a lot better.

[yat89]

Hi Jonnin, I had try the code on a new compiler which is Visual Studio 2017.

but the error still occurred.
Debug assertion failed.
Expression: Vector iterator range transposed

But when I change
reverse(route[row].begin() + (i1 + 2), route[row].begin() + i2);

to
reverse(route[row].begin() + i1, route[row].begin() + i2);
the code run well.

also if i change to
reverse(route[row].begin() + i1 + 1, route[row].begin() + i2)
the code also run well.