combine the C# code together and test program.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Projecttest
{
class Program
{
//Declare student structure
struct student

{
public string stnumber;

public string stname;

public string sex;

public float quizz1;

public float quizz2;

public float assigment;

public float midterm;

public float final;

public float total;


};

//main method
static void Main(string[] args)
{

try
{
student[] st = new student[20]; //create an array to store only 20 students'records for testing.
int itemcount = 0;
//show menu
displaymenu();
int yourchoice;
string confirm;

do
{

Console.Write("Enter your choice(1-8):");

yourchoice = int.Parse(Console.ReadLine());


switch (yourchoice)
{

case 1:add(st, ref itemcount); break;
case 2:delete(st, ref itemcount); break;
case 3:update(st, itemcount); break;
case 4:viewall(st, itemcount); break;
case 5:average(st, itemcount ); break;
case 6:showmax(st, itemcount); break;
case 7:showmin(st, itemcount); break;
case 8:find(st, itemcount); break;
case 9: bubblesort (st, itemcount); break; 

default: Console.WriteLine("invalid"); break;

}



Console.Write("Press y or Y to continue:");

confirm = Console.ReadLine().ToString();

} while (confirm == "y" || confirm == "Y");



}
catch (FormatException f) { Console.WriteLine("Invalid input"); }


///////////////

Console.ReadLine();

}


//Menu contruction

static void displaymenu(){

Console.WriteLine("=====================================================");

Console.WriteLine(" MENU ");

Console.WriteLine("=====================================================");

Console.WriteLine(" 1.Add student records");
Console.WriteLine(" 2.Delete student records");
Console.WriteLine(" 3.Update student records");
Console.WriteLine(" 4.View all student records");
Console.WriteLine(" 5.Calculate an average of a selected student's scores");
Console.WriteLine(" 6.Show student who get the max total score"); 
Console.WriteLine(" 7.Show student who get the min total score");
Console.WriteLine(" 8.Find a student by ID");
Console.WriteLine(" 9.Sort students by TOTAL");



}
//method add/append a new record
static void add(student[] st,ref int itemcount){

Again:
Console.WriteLine(); 
Console.Write("Enter student's ID:");
st[itemcount].stnumber=Console.ReadLine().ToString() ;

if(search(st,st[itemcount].stnumber,itemcount)!=-1){

Console.WriteLine("This ID already exists.");
goto Again;

}


Console.Write("Enter student's Name:"); 

st[itemcount].stname=Console.ReadLine ().ToString();


Console.Write("Enter student's Sex(F or M):");
st[itemcount].sex=Console.ReadLine().ToString();


Console.Write("Enter student's quizz1 score:");
st[itemcount].quizz1=float.Parse(Console.ReadLine());


Console.Write("Enter student's quizz2 score:");
st[itemcount].quizz2=float.Parse(Console.ReadLine());


Console.Write("Enter student's assigment score:");
st[itemcount].assigment=float.Parse(Console.ReadLine());


Console.Write("Enter student's mid term score:");
st[itemcount].midterm=float.Parse(Console.ReadLine());

Console.Write("Enter student's final score:");
st[itemcount].final=float.Parse(Console.ReadLine());

st[itemcount].total=st[itemcount].quizz1+st[itemcount].quizz2+st[itemcount].assigment+st[itemcount].midterm+st[itemcount].final;



++itemcount;



}
//method to search for the location of the target record
static int search(student[] st, string id,int itemcount){
int found =-1;
for (int i = 0; i < itemcount && found==-1; i++)
{

if (st[i].stnumber == id) found=i;

else found=-1 ;
}

return found;

}
//method display all students' records
static void viewall(student[] st,int itemcount)
{

int i = 0;

Console.WriteLine("{0,-5}{1,-20}{2,-5}{3,-5}{4,-5}{5,-5}{6,-5}{7,-5}{8}(column index)", "0", "1", "2", "3", "4", "5", "6", "7", "8");
Console.WriteLine("{0,-5}{1,-20}{2,-5}{3,-5}{4,-5}{5,-5}{6,-5}{7,-5}{8,-5}", "ID", "NAME", "SEX", "Q1", "Q2", "As", "Mi", "Fi", "TOTAL");

Console.WriteLine("=====================================================");

while (i < itemcount)
{

if (st[i].stnumber !=null )
{

Console.Write("{0,-5}{1,-20}{2,-5}", st[i].stnumber, st[i].stname, st[i].sex);

Console.Write("{0,-5}{1,-5}{2,-5}",st[i].quizz1,st[i].quizz2,st[i].assigment);

Console.Write("{0,-5}{1,-5}{2,-5}",st[i].midterm,st[i].final,st[i].total);

Console.Write("\n");
}

i = i + 1;



}

}



// method to elete record

static void delete(student[] st, ref int itemcount)
{
string id;
int index;
if (itemcount > 0)
{
Console.Write("Enter student's ID:");
id = Console.ReadLine();
index = search(st, id.ToString(),itemcount); 

if ((index!=-1) && (itemcount != 0))
{
if (index == (itemcount-1)) //delete the last record
{

clean(st, index);
--itemcount;

Console.WriteLine("The record was deleted.");
}
else //delete the first or middle record
{
for (int i = index; i < itemcount-1; i++)
{
st[i] = st[i + 1];
clean(st, itemcount);
--itemcount ;
}

}

}
else Console.WriteLine("The record doesn't exist.Check the ID and try again.");


}
else Console.WriteLine("No record to delete");
}

//method ot update record

static void update(student[] st, int itemcount)
{
string id;
int column_index;
Console.Write("Enter student's ID:");
id=Console.ReadLine();
Console.Write("Which field you want to update(1-7)?:");
column_index=int.Parse(Console.ReadLine());

int index = search(st, id.ToString(),itemcount);

if ((index != -1) && (itemcount != 0))
{
if (column_index == 1)
{
Console.Write("Enter student's Name:");

st[index].stname = Console.ReadLine().ToString();
}

else if (column_index == 2)
{
Console.Write("Enter student's Sex(F or M):");
st[index].sex = Console.ReadLine().ToString();
}
else if (column_index == 3)
{
Console.Write("Enter student's quizz1 score:");
st[index].quizz1 = float.Parse(Console.ReadLine());
}
else if (column_index == 4)
{
Console.Write("Enter student's quizz2 score:");
st[index].quizz2 = float.Parse(Console.ReadLine());
}
else if (column_index == 5)
{
Console.Write("Enter student's assigment score:");
st[index].assigment = float.Parse(Console.ReadLine());
}
else if (column_index == 6)
{
Console.Write("Enter student's mid term score:");
st[index].midterm = float.Parse(Console.ReadLine());
}
else if (column_index == 7)
{
Console.Write("Enter student's final score:");
st[index].final = float.Parse(Console.ReadLine());
}
else Console.WriteLine("Invalid column index");
st[index].total = st[index].quizz1 + st[index].quizz2 + st[index].assigment + st[index].midterm + st[index].final;


}
else Console.WriteLine("The record deosn't exits.Check the ID and try again.");

}


//method to calculate average score
static void average(student[] st, int itemcount)
{
string id;
float avg=0;
Console.Write("Enter students'ID:");
id = Console.ReadLine();
int index = search(st, id.ToString(),itemcount);
if (index != -1 && itemcount>0)
{
st[index].total = st[index].quizz1 + st[index].quizz2 + st[index].assigment + st[index].midterm + st[index].final;
avg = st[index].total /5;
}

Console.WriteLine("The average score is {0}.", avg);
}
//method to show max total score 
static void showmax(student[] st, int itemcount)
{
float max = st[0].total;
int index=0;
Console.WriteLine(itemcount);
if (itemcount >= 2)
{

for (int j = 0; j < itemcount-1; ++j)
if (max < st[j+1].total) {
max = st[j+1].total;
index = j+1;

}


}

else if (itemcount == 1)
{
index = 0;
max = st[0].total;
}


else Console.WriteLine("Not record found!");

if (index != -1) Console.WriteLine("The student with ID:{0} gets the highest score {1}.", st[index].stnumber, max);


}
//method to show min total score
static void showmin(student[] st, int itemcount)
{

float min = st[0].total;
int index = 0;
if (itemcount >= 2)
{
for (int j = 0; j < itemcount-1; ++j)
if (min > st[j+1].total)
{
min = st[j+1].total;
index = j+1;

}



}

else if (itemcount == 1)
{
index = 0;
min = st[0].total;
}
else Console.WriteLine("No record found!");

if (index != -1) Console.WriteLine("The student with ID:{0} gets the lowest score {1}.", st[index].stnumber, min);


}
//method to find record
static void find(student[] st, int itemcount)
{
string id;
Console.Write("Enter student's ID:");
id=Console.ReadLine();

int index=search(st,id.ToString(),itemcount);
if (index != -1)
{
Console.Write("{0,-5}{1,-20}{2,-5}", st[index].stnumber, st[index].stname, st[index].sex);

Console.Write("{0,-5}{1,-5}{2,-5}", st[index].quizz1, st[index].quizz2, st[index].assigment);

Console.Write("{0,-5}{1,-5}{2,-5}", st[index].midterm, st[index].final, st[index].total);
Console.WriteLine(); 

}
else Console.WriteLine("The record doesn't exits.");

}


//method to sort records by total score
static void bubblesort(student[] dataset, int n)
{
int i, j;
for (i = 0; i < n; i++)
for (j = n - 1; j > i; j--)
if (dataset[j].total < dataset[j - 1].total )
{
student temp = dataset[j];
dataset[j] = dataset[j - 1];
dataset[j - 1] = temp;
}

}
//method to clean deleted record
static void clean(student[] st,int index)
{
st[index].stnumber = null;
st[index].stname = null;
st[index].sex = null;
st[index].quizz1 = 0;
st[index].quizz2 = 0;
st[index].assigment = 0;
st[index].midterm = 0;
st[index].final = 0;
st[index].total = 0;

}


}
}