Iterating over 2D vector using -> (arrow) and replacing the values: C++

Question

I am trying to use iterators to go through 2D vector and replace a specific symbol with another symbol. If you take a look at the first code bellow you will notice that there is no problem to replace '.' with '+' (in standard vector), However: if I try the same approach with a 2D vector the compiler shows me the following error: vec.at(col - row->begin()) = '+'; Compiler Error C2679 binary 'operator': no operator found which takes a right-hand operand of type 'type' (or there is no acceptable conversion)

#include <iostream>
#include <vector>
#include <iterator>

using namespace std;

int main()
{
    vector<char> myints{ '.', '.','!','.' };
    vector<char>::iterator p;

    p = find(begin(myints), end(myints), '!');

    if (p != end(myints)) {
        myints.at(p - begin(myints)) = '+';
    }

    for (auto i : myints) {
        cout << i << " ";
    }

    return 0;
}

and the following:

#include <iostream>
#include <vector>
#include <iterator>

using namespace std;


void readVector(vector< vector<char> >& vec)
{
    vector< vector<char> >::iterator row;
    vector<char>::iterator col;

    for (row = vec.begin(); row != vec.end(); ++row)
    {
        for (col = row->begin(); col != row->end(); ++col) {

            if (*col == '!') {
                vec.at(col - row->begin()) = '+';
            }
        }
    }
}

int main()
{
    // Initializing 2D vector "vect" with 
    // values 
    vector<vector<char> > vect{ { '.', '.', '.' },
                               { '!', '.', '.' },
                               { '!', '.', '!' } };

    readVector(vect);
}

Thanks a lot in advance!

Answer 1

Modify offending line to

            row->at(col - row->begin()) = '+';

You've addressing the index of a row and not in the original vec .

On a side note your first program can be simplified to be used with many different containers with this change, no just random access containers.

   p = find(begin(myints), end(myints), '!');
   if (p != end(myints)) {
      *p = '+';
   }

The same goes to the offending line:

        if (*col == '!') {
            *col = '+';
         }