Error must have class type - c++

Question

I'm kinda new in C++ and when trying to compile this code I get and error that I do not know how to fix:
int main()
{
typedef pair<int,int> nodo;
int x;
cin >> x;
int *g;
g = new int[x];
vector <nodo> g;
g[1].push_back(nodo(2,5));
g[1].push_back(nodo(3,10));
g[3].push_back(nodo(2,12));
g[2].push_back(nodo(4,1));
g[4].push_back(nodo(3,2));
for (int i = 1; i <=4; ++i){
// cout << i << " -> ";
for (int j = 0; j<g[i].size(); ++j){
// cout << g[i][j].first << " c: " << g[i][j].second << " ";
}
// cout << endl;
}
dijkstra(1, x);
system("pause");
return 0;
}
The error I am receiving is:
Error: Expression must have a class type.

Answer 1

Here:
int *g;
g = new int[x];
vector <nodo> g; // ERROR: Redeclaration!
You are first declaring g to be of type int*, and then you re-declare it to be of type vector<nodo>. This is illegal.
Moreover, you need to have a using namespace std directive if you want to omit the std:: qualification for types in the standard namespace. I do not suggest you using that though. Much better explicitly specifying std::, or rather use specific using declarations.
For instance:
typedef std::pair<int,int> nodo;
// ^^^^^
int x;
std::cin >> x;
// ^^^^^
int *g;
g = new int[x];
std::vector <nodo> g;
// ^^^^^
Also make sure you are importing all the necessary standard headers:
Type | Header
--------------------------
std::vector -> <vector>
std::pair -> <utility>
std::cin -> <iostream>

Answer 2

You're redeclaring g, first it's an int* and then you make it into a vector<int>. I'm not sure how that got past the compiler.
Also, rather than using nodo(1,2) consider using make_pair instead. Using new is also considered bad practice and you should use either a dynamic container like std::vector or a static one like std::array.

Answer 3

You have two things named g:
int* g;
and
vector <nodo> g;
This wouldn't even compile.
It looks like you want an array of vectors, in which case you need something like
std::vector<std::vector<nodo> > g(x); // size x vector of vectors.
Then you can do this type of thing:
g[1].push_back(nodo(2,5));
g[1].push_back(nodo(3,10));

Answer 4

pair is not a class because you haven't included <utility>
You also haven't included <vector> or <iostream>.

Answer 5

So this version compiles and I think this is what you meant to do:
// Need to include these headers
#include <utility>
#include <iostream>
#include <vector>
using namespace std;
int main()
{
typedef pair<int,int> nodo;
int x;
cin >> x;
//int *h;
//h = new int[x];
//specify size of vector
std::vector< std::vector<nodo> > g(x);
g[0].push_back(nodo(2,5));
g[1].push_back(nodo(3,10));
g[2].push_back(nodo(2,12));
g[3].push_back(nodo(4,1));
g[4].push_back(nodo(3,2));
for (int i = 0; i < g.size(); ++i){
std::cout << i << " -> ";
for (int j = 0; j<g[i].size(); ++j){
cout << g[i][j].first << " c: " << g[i][j].second << " ";
}
cout << endl;
}
//dijkstra(1, x);
//system("pause");
return 0;
}
Many issues, you use g twice for one. I am not sure what you want to do with the vector but maybe you want a vector of vectors which would be more like this:
std::vector< std::vector<nodo> > g(x) ;
Then this would make more sense:
g[0].push_back(nodo(2,5)) ;
The first element of a vector is going to be at 0 not 1.