Member function and expected primary-expression errors - c++

Question

Here is my code, I am currently working on my own BigInt class and I am having some problems with getters and setters, and some program structure.
I keep getting these two errors:
prog.cpp: In function 'int main()':
prog.cpp:38:29: error: cannot call member function 'void bigInt::setString(std::string)' without object
bigInt::setString(digString);
^
prog.cpp:39:28: error: expected primary-expression before 'void'
cout << bigInt::getString(void);
^
Code
//my bigInt class
#include <iostream>
#include <vector>
#include <string>
using namespace std;
//class, constructors
//overload operators methods
//add, subtract, multiply, divide
class bigInt{//class
public:
bigInt();
~bigInt();
void setString(string dig);
string getString(void);
std::string digit;
std::string digString;
private:
std::vector<int> big1;
std::vector<int> big2;
};
//constructors
bigInt::bigInt(void){
}
//deconstructor
bigInt::~bigInt(){
}
void bigInt::setString(string dig){
digit= dig;
}
string bigInt::getString(){
return digit;
}
int main(){
string digString= "90867537465982736459087162745938";
bigInt::setString(digString);
cout << bigInt::getString(void);
}
Thanks in advance!

Answer 1

In main you would do something like.
int main(){
string digString= "90867537465982736459087162745938";
bigInt my_int{};
my_int.setString(digString);
cout << my_int.getString();
}
You have to actually instantiate a bigInt object, which I called my_int in the above example. Then you can call the methods setString() and getString() off of that object.
The only class methods that you can call without having an instance to call them off of are static methods.

Answer 2

You need an object to work with. Try in your main:
bigInt myInt;
myInt.setString(...);