Improper use of typedef

Anyone knows what does these errors mean ?


Error E2108 workingArea.cpp 61: Improper use of typedef 'string' in function newCode()
Error E2121 workingArea.cpp 61: Function call missing ) in function newCode()
*** 2 errors in Compile ***

Code:

---

int main()
{
        string billy [12];
        int tester;
                while((tester >= 1) || (tester < 4))
                {
                        cout << "select one of these options\n";
                        cout << "(1) Insert a new code\n";
                        cout << "(2) Print the data\n";
                        cout << "(3) Program requirments\n";
                        cout << "(4) Exit the program\n";

                        cin >> tester;
                       
                        if(tester==1)
                                newCode();               
                        else if (tester==2)
                                printCode();
                        else if (tester==3)
                                errorCode();       
                        else if (tester==4)
                                break;
                        else
                                cout << "ERROR!!! You must choose one of the options from 1 to 4";
                }
return 0;

} 

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
void newCode()
{
        string serial_number;
        int length;       
         
  cout<< "please enter a serial number of 12 characters:";
        cin >> serial_number;
        length = serial_number.length();
       
        std::string mystr = serial_number;

        if (length!=12 )
                cout << "There must be 12 characters exactly";
        else
                checkOne(string serial_number);

}

void checkOne(        string serial_number)
{
        std::string mystr = serial_number;
        for( int i=0; i<13;i++)
        {
                if( mystr[i]!= '4')
                        break;
                        cout << "correct"<<endl;
        }
               
}

---

> checkOne(string serial_number);
Your call is wrong.
Remove the type.

I deleted the type but a bunch of errors showed up are the following:

Error E2268 workingArea.cpp 61: Call to undefined function 'checkOne' in function newCode()
Warning W8054 workingArea.cpp 65: Style of function definition is now obsolete
Error E2238 workingArea.cpp 67: Multiple declaration for 'serial_number' in function checkOne()
Warning W8057 workingArea.cpp 76: Parameter 'serial_number' is never used in function checkOne()
*** 2 errors in Compile ***


All what I want to do is to use the ( serial_number) and the ( mystr) in the (void checkOne()) method from the ( void newCode()) method. This is also the first part that I did not post:

Code:

---

#include <iostream>
#include <cctype>
#include<string>
#include <stdio.h>
#include <stdlib.h>
using namespace std;

void newCode();
void printCode();
void errorCode();
//void checkOne();

string billy [12];

---

a) you need to prototype your functions
b) you need to make sure the parameters match in the prototype and the definition.