GPa Calculator in c++

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

void main()
{
char number[40] ={0};           //this array use to store enrollment number
char name[40] ={0}; // this array use to store students name
float arr[9] = {0}; // this array use to store number and gpa



float gpa,s = 0; // declare variable,,"s" variable use to store credit hours of every subject
int totalcredithours=18; // total credit hours



for(int p=0;p<1;p++) // this loop depend on number of students in class

{   // start braces for loop "p"
gpa = 0;

cout<<"\t\t\tEnrollment Number:";


cin.ignore();
cin.getline(number,80,'\n');


cout<<"\t\t\tStudent Name:";


cin.ignore();
cin.getline(name,80,'\n');




for(int i=1;i<=8;i++) // this loop run only 6 times to get subject number and this loop use only in switch statement

 { // start braces for loop "i"


int x; //declare variable to get number from user



switch(i) //conditional statement


{   // start braces for switch statement

case 1:
cout<<"\n\t\t\tDiscrete Structures "<<endl;
cout<<"\t\t\tEnter Number=";
s=0+3;
break;


case 2:
cout<<"\t\t\tObject Oriented Programming"<<endl;
cout<<"\t\t\tEnter Number=";
s=0+3;
break;


case 3:
cout<<"\t\t\tCommunication Skills"<<endl;
cout<<"\t\t\tEnter Number=";
s=0+3;
break;


case 4:
cout<<"\t\t\tBasic electronics"<<endl;
cout<<"\t\t\tEnter Number=";
s=0+2;
break;

case 5:
cout<<"\t\t\tPakistan Studies"<<endl;
cout<<"\t\t\tEnter Number=";
s=0+2;
break;

case 6:
cout<<"\t\t\tscoiology"<<endl;
cout<<"\t\t\tEnter number=";
s=0+3;
break;

case 7:
cout<<"\t\t\tObject Oriented Programming lab"<<endl;
cout<<"\t\t\tEnter number=";
s=0+1;
break;

case 8:
cout<<"\t\t\tBasic electronics lab"<<endl;
cout<<"\t\t\tEnter number=";
s=0+1;
break;





default:
cout<<"\t\t\tNot Valid";


} //end braces for switch statement



cin>>x;   //get numbers from user



//now we using if else statements to check grades


if(x>=87&&x<=100)
{
cout<<"\t\t\tGrade A"<<endl<<endl;
arr[i] = (4.0)*s;
}

else if(x>=79&&x<=86)
{
cout<<"\t\t\tgrade B+"<<endl<<endl;
arr[i] = (3.5)*s;
}

else if(x>=72&&x<=79)
{
cout<<"\t\t\tgrade B"<<endl<<endl;
arr[i] = (3.0)*s;
}

else if(x>=66&&x<=71)
{
cout<<"\t\t\tgrade c+"<<endl<<endl;
arr[i] = (2.5)*s;
}

else if(x>=60&&x<=65)
{
cout<<"\t\t\tgrade c"<<endl<<endl;
arr[i] = (2.0)*s;
}

else if(x>=50&&x<=59)
{
cout<<"\t\t\tgrade D"<<endl<<endl;
arr[i] = (1.5)*s;
}

else if(x<50&&x>=0)
{
cout<<"\t\t\tgrade F"<<endl<<endl;
arr[i] = (0)*s;
}

else if(x>100)
{
cout<<"\t\t\tPlease Enter Numbers '0' to '100'"<<endl<<endl;
}

if(x<0)
{
cout<<"\t\t\tPlease Enter Numbers '0' to '100'"<<endl<<endl;
}


} //end for loop "i"





float sum = 0;

for(int j=1;j<=8;j++)

{     // start braces for loop "j"

sum+= arr[j];

}    // end braces for loop "j"



gpa=(sum)/totalcredithours;                 //formula to calculate gpa
cout<<"\t\t\tGPA="<<gpa<<endl<<endl;


if(gpa<2.0&&gpa>1.5)

{
cout<<"\t\t\tprob :(";
}

else if(gpa<1.5&&gpa>1.0)

{
cout<<"\t\t\tchance :(";
}


 } //end braces for loop "p"


 } //end braces main funtion