error C2679: binary '<<': no operator found which takes a right-hand operand of type 'std::vector<int,std::allocator<_Ty>>'

[sarah1993]

Hi everyone, I'm new to C++. I've been assigned the following tasks.
1. Choose any two random numbers in the range 3 to 9.
2. Find position of these random numbers for each row.
3. Swap these two random numbers for each row.
4. Display new vector after swapping.

I tried to solve it but error occurred.
Error:
error C2679: binary '<<': no operator found which takes a right-hand operand of type 'std::vector<int,std::allocator<_Ty>>' (or there is no acceptable conversion)

I don't know how to fix it. Hopefully someone can help me. Thank you :)

#include <iostream>     // cout
#include <ctime>		// time
#include <cstdlib>		// srand, rand()
#include <algorithm>    // find(), iter_swap()
#include <vector>       // vector

using namespace std;

int main()
{
	// Initialize random seed:
	srand(time(NULL));

	vector< vector<int> > vec =
	{
		{ 9, 8, 7, 6, 5, 4, 3, 2, 1 },
		{ 1, 2, 3, 4, 5, 6, 7, 8, 9 },
		{ 5, 4, 3, 2, 1, 9, 8, 7, 6 }
	};

	// Print Original Vector
	cout << "Original vector :" << endl;
	for (size_t i = 0; i < vec.size(); i++)
	{
		for (size_t j = 0; j < vec[i].size(); j++)
		{
			cout << vec[i][j] << " ";
		}
		cout << "\n";
	}
	
	// Generate two random number in the range 3 to 9
	int r1, r2;
	do {
		r1 = rand() % 9 + 3;      // r1 in the range 3 to 9
		r2 = rand() % 9 + 3;	// r2 in the range 3 to 9
	} while (r1 == r2);

	cout << "First random number = " << r1 << endl;
	cout << "Second random number = " << r2 << endl;

	// Iterator used to store the position of searched element
	

	for (size_t i = 0; i < vec.size(); i++)
	{
		vector <vector<int> >::iterator it, ik;

		// Find position of first random number, r1
		it = find(vec.begin(), vec.end(), r1);
		if (it != vec.end())
		{
			cout << "First random number " << r1 << " was found at position ";
			cout << it - vec.begin() + 1 << "\n";
		}
		else
			cout << "Number not found.\n\n";

		// Find position of second random number, r2
		ik = find(vec.begin(), vec.end(), r2);
		if (ik != vec.end())
		{
			cout << "Second random number " << r2 << " was found at position ";
			cout << ik - vec.begin() + 1 << "\n";
		}
		else
			cout << "Number not found.\n\n";

		// Swap them
		if (it != vec.end() && ik != vec.end())
		{
			cout << "Swapping random numbers " << *it << " and " << *ik << '\n';
			iter_swap(it, ik);
		}

		// Print New Vector
		cout << "New vector :";
		for (size_t i = 0; i < vec.size(); i++)
		{
			for (size_t j = 0; j < vec[i].size(); j++)
			{
				cout << vec[i][j] << " ";
			}
			cout << "\n";
		}
	}

	return 0;
}

[helios]

Here:

cout << "Swapping random numbers " << *it << " and " << *ik << '\n';

The type of it is std::vector<std::vector<int>>::iterator, so the type of *it is std::vector<int>.

Are you sure the rest of the code in the loop does what you think it does? What it really does is not swap two numbers. It's swapping two vectors; two rows, if you will.

[lastchance]

Because you have a vector of vectors, your iterators are pointing to an entire vector of values, not a single value ... so the << operator won't know how to output them.

Perhaps you would like to explain exactly how you think "your" code works?

I think it would be easier to advise if you gave us VERBATIM the bit of your assignment BEFORE what you have quoted: we are only getting a very confused story and it is unclear what you are being asked.

[sarah1993]

HiHelios,

Are you sure the rest of the code in the loop does what you think it does? What it really does is not swap two numbers. It's swapping two vectors; two rows, if you will.

Can't I use iter_swap() function to swap numbers?

Hilastchance,

I think it would be easier to advise if you gave us VERBATIM the bit of your assignment BEFORE what you have quoted: we are only getting a very confused story and it is unclear what you are being asked.

Sorry for inconvenience. I was given a task to generate two random numbers between 3 to 9.
For example: first random number = 5 and second random number = 9.

Then, I need to find the position of these random number for each row vector as follow:
{ 9, 8, 7, 6, 5, 4, 3, 2, 1 } --> first random number = position 5, second random number = position 1
{ 1, 2, 3, 4, 5, 6, 7, 8, 9 } --> first random number = position 5, second random number = position 9
{ 5, 4, 3, 2, 1, 9, 8, 7, 6 } --> first random number = position 1, second random number = position 6.

Then, swap these random numbers for each row
{ 9, 8, 7, 6, 5, 4, 3, 2, 1 } --> { 5, 8, 7, 6, 9, 4, 3, 2, 1 }
{ 1, 2, 3, 4, 5, 6, 7, 8, 9 } --> { 1, 2, 3, 4, 9, 6, 7, 8, 5 }
{ 5, 4, 3, 2, 1, 9, 8, 7, 6 } --> { 9, 4, 3, 2, 1, 5, 8, 7, 6 }

[lastchance]

You need to deal with each vec[i] in turn, not the whole of vec.

I presume you know whether the number refers to the value or its position.

[sarah1993]

Hi lastchance,

You need to deal with each vec[i] in turn, not the whole of vec.

Does it mean I need to deal with each column not each row.

Sorry for asking. A bit confusing..

[helios]

Does it mean I need to deal with each column not each row.

You need to deal with both.

[lastchance]

sarah1993 wrote:

Does it mean I need to deal with each column not each row.

You need to deal with the i'th row (that, is, vec[i]) inside the i loop.

		vector <vector<int> >::iterator it, ik;
		// Find position of first random number, r1
		it = find(vec.begin(), vec.end(), r1);

needs to be

		vector<int>::iterator it, ik;
		// Find position of first random number, r1
		it = find(vec[i].begin(), vec[i].end(), r1);

with a whole mass of other changes from vec to vec[i] below it.


For your final output either move it outside the i loop, or just do one row vector at a time.

Your random numbers are currently in the range 3 to 11, not 3 to 9.

[sarah1993]

Hi lastchance and helios, thank you for your advise.

I've improved this codes based on your explanation and it worked. Thank you so much for helping. I really appreciated it.