Replace data in 2D vector C++ - c++

Question

I am trying to search a 2D vector for a char, namely a '?' and replace it with 'x'.
I have no issues doing this task with a single vector but keep having issues with the a 2D vector implementation, see below for code.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
// An empty vector of vectors
vector<vector<char> > v2d;
// Create a vector with 5 elements
vector<char> v2(5, '?');
// Create a vector of 3 elements.
vector<vector<char> > v2d2(3, v2);
// Print out the elements
cout << "Before Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
cout << v2d2[i][j] << " ";
cout << endl;
}
cout << "" << endl;
/* Does not work as expected
cout << "Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
{
if (v2d[i] == '?');
(v2d[i] = 'x');
}
}
*/
cout << "" << endl;
cout << "After Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
cout << v2d2[i][j] << " ";
cout << endl;
}
system("pause > NULL");
return 0;
}
I receive the error message below when I try and compile the code.
IntelliSense: no operator "==" matches these operands operand types are: std::vector>, std::allocator>>> == char Project3\Source.cpp 77 16 Project3
I believe it is an issue with the container in updating the proper row and column. Any help would be much appreciated.
Thank you

Answer 1

There were a few bugs, please compare with your original code:
#include <iostream>
#include <vector>
using namespace std;
int main()
{
// An empty vector of vectors
vector<vector<char> > v2d;
// Create a vector with 5 elements
vector<char> v2(5, '?');
// Create a vector of 3 elements.
vector<vector<char> > v2d2(3, v2);
// Print out the elements
cout << "Before Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
cout << v2d2[i][j] << " ";
cout << endl;
}
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
if (v2d2[i][j] == '?')
v2d2[i][j] = 'x';
}
cout << "After Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
std::cout << v2d2[i][j] << " ";
cout << endl;
}
return 0;
}

Answer 2

Take a look at your commented code:
cout << "Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
{
if (v2d[i] == '?'); // <------
(v2d[i] = 'x');
}
}
There is a semi-colon after the if statement, meaning that nothing will be executed if the statement is true. Rookie mistake.
Many consider it a bad practice not to always use parentheses with if-statements and other similar situations that require them, because of issues like this one

Answer 3

You should have :
if (v2d[i][j] == '?'){
v2d[i][j] = 'x';
}

Answer 4

cout << "Vector Update" << endl;
for (int i = 0; i < v2d2.size(); i++) {
for (int j = 0; j < v2d2[i].size(); j++)
{
if (v2d[i][j] == '?')
v2d[i][j] = 'x';
}
}
You were not accessing the 2d vector correctly, should have used v2d[i][j] instead.