Grade Statistics C++

#include
using namespace std;

const int MaxSize=100;
int actualNum=8;
string studentID[MaxSize]={"p1001","p1002","s000101","s000102","s000135","s990001","s990002","s000103"};
double studentMark[MaxSize]={78.5, 66, 73, 56.5, 88.3, 64.5, 45, 57};
char studentGrade[MaxSize]={'D', 'C', 'C', 'P', 'H', 'P', 'F', 'P'};

void do_again(),direction(int ans);
void option_1(),option_2(),option_3(),option_4();

int main()
{

do_again();//call do_again function, say goodbye to main until everything else is done running

return 0;
}//end function

void do_again()
{
int ans;//declare ans variable, this will be used OVER AND OVER
do
{
cout << "MAIN MENU\n\n";
cout << "1. Exit ";
cout << "2. Statistics\n";
cout << "3. Enter mark ";
cout << "4. Find mark\n\n";
cout << "Please choose a number to enter: ";

cin >> ans;
while (cin.fail())
{cout << "Wrong data type! Re-enter: ";
cin.clear();
cin.ignore(80,'\n'); //Take in an answer
cin>>ans; cout< }
direction(ans);//Send that answer to direction
}while(ans!=1);//Keep on keeping on until they press 1 to exit
}//end function

void direction(int ans)
{
switch (ans)//roll thru options
{
case 1: //if they picked the number 1, its gonna go to this function,
option_1();
break;
case 2:
option_2();
break;
case 3:
option_3();
break;
case 4:
option_4();
break;
default://THEY DID NOT READ THE MENU, WHO WOULD HAVE THOUGHT?
cout << "Please press 2, 3 or 4. Press 1 for close the menu.\n\n";
//break;
}
}//end function

//functions, FILL WITH VALUABLE PROGRAMMING SKILLS

void option_1()
{
}//end function

void option_2()
{

}//end function

void option_3()
{
double mark;
char grade;
string id;
cout << "\n\n";
cout << "ENTER MARK MENU\n\n";
cout << "Enter the ID: ";
cin >> studentID[actualNum];
cout << "Enter the mark: ";
cin >> mark;
studentMark[actualNum]=mark;
cout << "\n\n";

if (mark<=100 && mark>=0)
{
if (mark>=85)
// cout << "The mark " << mark << " is: H\n\n\n";
studentGrade[actualNum]='H';
else if (mark>=75)
// cout << "The mark " << mark << " is: D\n\n\n";
studentGrade[actualNum]='D';
else if (mark>=65)
// cout << "The mark " << mark << " is: C\n\n\n";
studentGrade[actualNum]='C';
else if (mark>=50)
// cout << "The mark " << mark << " is: P\n\n\n";
studentGrade[actualNum]='P';
else
// cout << "The mark " << mark << " is: F\n\n\n";
studentGrade[actualNum]='F';
}
else
studentGrade[actualNum]='I'; // Error

++actualNum;
}//end function

void option_4()
{
int i=-1;
string id;
cout << "\n\n";
cout << "FIND MARK MENU\n\n";
cout << "Enter your student ID: ";
cin >> id;

while(++i if(id==studentID[i])
{cout << "Your mark is: " << studentMark[i] << " and your grade is: " << studentGrade[i];
cout << "\n\n";
break;}
}
if (i==actualNum)
cout<<"Sorry, it is not existing."< cout << "\n\n";

} //end function