CODEWITHSUNDEEP
c++vectoriteration
user2943507
user2943507

Reputation: 91

Iterating through a 2d Vector row

I am working on a homework assignment for my C++ class.

I am trying to iterate through a 2d multidimensional vector. I have all the data in the 2d vector which is size 7x7 i.e. 0-6 by 0-6,.

Problem is I need to output the contents of the 2d vector in the order of alphaV[0][0], alphaV[1][0], alphaV[2][0], etc.

When I try to use a nested For loop to process this vector I run into problems whereby the rows of the vector will not iterate, that is to say they remain at index 0.

So it keeps repeating alphaV[0][0], alphaV[0][0], alphaV[0][0], etc.

How do I go about iterating the columns in that pattern [0][0], [1][0], [2][0] ...?

Upvotes: 8

Views: 27427

Answers (2)

Aylian Craspa
Aylian Craspa

Reputation: 466

Only for giving complete example for the AngelCastillo's answer

#include <iostream>
#include <vector> 

using namespace std; //to stop using std every time

int main(){
    vector<int> vts;
    vector<vector<int>> vec; //multidimensional vector
    
//simple vector iteration
    vts.push_back(10);
    for(vector<int>::iterator itv = vts.begin();itv != vts.end(); ++itv ){
        cout << *itv << "\n";
    }

//how to add multidimensional objects
    vector<int> tmp;
    tmp.push_back(20);
    vec.push_back(tmp);
    
    vector<vector<int>>::const_iterator row; 
    vector<int>::const_iterator col; 

    for (row = vec.begin(); row != vec.end(); ++row)
    { 
         for (col = row->begin(); col != row->end(); ++col)
         { 
            cout << *col << "\n"; 
         } 
    } 
    
//same iteration another way
    for(vector<vector<int>>::iterator row = vec.begin();row != vec.end(); ++row ){
        for(vector<int>::iterator col = row->begin();col != row->end(); ++col ){
            cout << *col << "\n"; 
        }
    }
}

Upvotes: 1

AngelCastillo
AngelCastillo

Reputation: 2435

Iterate over the vectors, this is the standard way of traversing containers:

void printVector(const std::vector< std::vector<int> > & vec)
{ 

    std::vector< std::vector<int> >::const_iterator row; 
    std::vector<int>::const_iterator col; 

    for (row = vec.begin(); row != vec.end(); ++row)
    { 
         for (col = row->begin(); col != row->end(); ++col)
         { 
            std::cout << *col; 
         } 
    } 

}

More information on iterators can be found here: http://www.cplusplus.com/reference/iterator/

Upvotes: 17

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