LNK2019 unresolved external symbol "int __cdecl examAvg(void)" - c++

Question

When I try to compile, I get only two error messages.
"Error LNK2019 unresolved external symbol "int __cdecl examAvg(void)" (?examAvg##YAHXZ) referenced in function _main
Line 1
and
LNK1120 1 unresolved externals
also on Line 1
I have worked on this so long (days) that I really can't figure out where I am going wrong anymore, I am sure it is something simple, but I am for a loss again.
Will someone please give me a suggestion to help rectify the error codes?
/*
Christopher Pierce
Date Created: July 3, 2020
Egrades Vector Application
*This application creates a C++ menu program that generates an electronic grade sheet that can keep track of five student test scores earned during the semester.
• Organizes the main program menu to call four functions.
• (1) function that allow a user to Add five students and their scores on three exams into the vector.
• (2) function that will compute the average test score for each of the five students in the vector.
• (3) function that all the user to display a student average test scores searching for their name in the vector.
• (4) function that will compute the average of the average exams in the vector and display the result.
*/
#include <iostream>
#include <string>
#include <cstdlib>
#include <iomanip>
#include <vector>
#include <cmath>
#include <algorithm>
using namespace std;
// Declarations
int score1;
int score2;
int score3;
int score4;
int score5;
int score6;
int score7;
int score8;
int score9;
int score10;
int score11;
int score12;
int score13;
int score14;
int score15;
string student1;
string student2;
string student3;
string student4;
string student5;
int main()
{
vector <string> StudentFile;
vector <int> Egrades;
int average1 = (score1 + score2 + score3) / 3;
int average2 = (score4 + score5 + score6) / 3;
int average3 = (score7 + score8 + score9) / 3;
int average4 = (score10 + score11 + score12) / 3;
int average5 = (score13 + score14 + score15) / 3;
// Prototype (functions)
int examAvg();
{
StudentFile.insert(StudentFile.begin(), student1);
Egrades.insert(Egrades.begin(), average1);
StudentFile.push_back(student2);
Egrades.push_back(average2);
StudentFile.push_back(student3);
Egrades.push_back(average3);
StudentFile.push_back(student4);
Egrades.push_back(average4);
StudentFile.push_back(student5);
Egrades.push_back(average5);
}
/*
Start of Menu
*/
// Defines the width of the menu
const int menuWidth = 84;
// This is a loop structure for the menu box using ASCII
// This prints the top left corner of the menu box (ASCII)
cout << char(201);
// This prints the top border of the menu box (ASCII)
for (int column = 0; column < menuWidth; ++column) {
cout << char(205);
}
// This prints the top right corner of the menu box (ASCII)
cout << char(187);
cout << "\n";
// array with menu options
string menu[15];
menu[0] = " **************";
menu[1] = " *** MAIN MENU ***";
menu[2] = " **************";
menu[3] = " Please Choose From The Following Options:";
menu[6] = " 1. Add 5 Students to Egrades Vector:";
menu[8] = " 2. Compute Student Test Score Average:";
menu[10] = " 3. Search A Student Average Test Score:";
menu[12] = " 4. Compute The Average Of All 5 Student Exam Averages:";
menu[14] = " 5. Exit";
for (string option : menu)
{
cout << char(186) // print left border
<< setw(menuWidth) // set next item width
<< left // set next item aligment
<< option // print menu option string with width and aligment
<< char(186) << "\n"; // print right border
}
// This will print the bottom left corner of the menu box (ASCII)
cout << char(200);
// This prints the bottom border of the menu box (ASCII)
for (int column = 0; column < menuWidth; ++column) {
cout << char(205);
}
// This prints the bottom right corner of the menu box (ASCII)
cout << char(188);
cout << "\n\n";
/*
END OF MENU
*/
char selection;
cout << "\t\t\t Enter Your Selection: ", cin >> selection, cout << endl;
switch (selection)
{
case '1':
system("CLS");
cout << "Student Information Section:\n\n";
// Student 1 Info, captures name and scores
cout << "\nEnter Student 1 Name: \n";
cin >> student1;
cout << "\nEnter Exam 1 Score: ";
cin >> score1;
cout << "Enter Exam 2 Score: ";
cin >> score2;
cout << "Enter Exam 3 Score: ";
cin >> score3; examAvg();
// Student 2 Info, captures name and scores
cout << "\nEnter Student 2 Name:\n";
cin >> student2;
cout << "\nEnter Exam 1 Score: ";
cin >> score4;
cout << "Enter Exam 2 Score: ";
cin >> score5;
cout << "Enter Exam 3 Score: ";
cin >> score6; examAvg();
// Student 3 Info, captures name and scores
cout << "\nEnter Student 3 Name:\n";
cin >> student3;
cout << "\nEnter Exam 1 Score: ";
cin >> score7;
cout << "Enter Exam 2 Score: ";
cin >> score8;
cout << "Enter Exam 3 Score: ";
cin >> score9; examAvg();
// Student 4 Info, captures name and scores
cout << "\nEnter Student 4 Name:\n";
cin >> student4;
cout << "\nEnter Exam 1 Score: ";
cin >> score10;
cout << "Enter Exam 2 Score: ";
cin >> score11;
cout << "Enter Exam 3 Score: ";
cin >> score12; examAvg();
// Student 5 Info, captures name and scores
cout << "\nEnter Student 5 Name:\n";
cin >> student5;
cout << "\nEnter Exam 1 Score: ";
cin >> score13;
cout << "Enter Exam 2 Score: ";
cin >> score14;
cout << "Enter Exam 3 Score: ";
cin >> score15; examAvg();
cout << "\n\n******************************************************\n";
cout << "!!! INFORMATION HAS BEEN ADDED TO EGRADES VECTOR !!!\n";
cout << "******************************************************\n\n";
cout << "To Return To Main Menu:\n\n";
system("pause");
return main();
break;
case '2':
system("CLS");
for (unsigned int i = 0; i < Egrades.size(); ++i)
{
cout << Egrades[i] << endl;
}
cout << "To Return To Main Menu:\n\n";
system("pause");
return main();
break;
case '3':
system("CLS");
int score;
cout << "\nEnter A Students Name To Find Their Average:\n";
cin >> score;
if (cin >> student1)
{
cout << "Average Found:\n" << average1;
}
else if (cin >> student2)
{
cout << "Average Found:\n" << average2;
}
else if (cin >> student3)
{
cout << "Average Found:\n" << average3;
}
else if (cin >> student4)
{
cout << "Average Found:\n" << average4;
}
else if (cin >> student5)
{
cout << "Average Found:\n" << average5;
}
else
{
cout << "Average not found.\n";
}
cout << "To Return To Main Menu:\n\n";
system("pause");
return main();
break;
case '4':
system("CLS");
cout << "The Average of All Five Students Averages Are:\n\n";
cout << "|| " << (average1 + average2 + average3 + average4 + average5) / 5 << " ||\n\n";
cout << "To Return To Main Menu:\n\n";
system("pause");
return main();
break;
case '5':
exit(-1);
break;
default: cout << "\n Invalid selection\n\n";
}
return 0;
}