I made a vector of vectors and i wanted to take values from the user.I simply don't know what is the problem with it
why can't i use push_back() here
and if you have any other method than this please tell.
vector<vector<int>> v;
for(int i=0;i<n;i++)
{
v.push_back(i+1);
for(int j=0;j<n;j++)
{
v[i].push_back(j+1);
}
}
doing this gives me error
error: no matching function for call to 'std::vector<std::vector<int> >::push_back(int)'
v.push_back(i+1);
You declared a vector of vectors of the type std::vector<std::vector<int>>.
vector<vector<int>> v;
It means that elements of the vector v has the type std::vector<int> not int.
So the compiler issues an error message for this statement
v.push_back(i+1);
that does not make a sense.
You could use such a call provided that the class template std::vector had an implicit constrictor from an integer expression to the type std::vector. However such a constructor is explicit
explicit vector(size_type n, const Allocator& = Allocator());
Thus there is no implicit conversion from the parameter an expression supplied to the parameter n to the type std::vector<int>.
It seems you mean the following
vector<vector<int>> v;
for(int i=0;i<n;i++)
{
v.resize(i+1);
for(int j=0;j<n;j++)
{
v[i].push_back(j+1);
}
}
v.resize(i+1) - just vector<vector<int>> v(n); for crying out loud.It is because v is a vector containing a vector of ints. Meaning you can't push_back an integer as it wants an int vector.
vector<vector<int>> v;
for(int i=0;i<n;i++)
{
vector<int> v2;
for(int j=0;j<n;j++)
{
v2.push_back(j+1);
}
v.push_back(v2);
}
Now consider this code, it will work because you are creating a new vector of ints, v2. If you push v2 to v, it will work as v requires an int vector for push_back.
People like to overcomplicate things when answering. The idea here is that you have created a vector inside a vector. So the first vector takes a vector as an input, whereas the second vector takes an "int". Therefore, you shouldn't push an integer in the first vector but a VECTOR of integers.
