C++ GPA Calculator

#include<iostream>
using namespace std;
class gpa
{
private:
unsigned int marks;
double gpa12;
char subject[70];
int total;
float per;
public:
gpa(int totl,int mrks,float gp,char sub[] ):total(totl),marks(mrks),gpa12(gp)
{
strcpy(subject,sub);
}
gpa():marks(0),total(0)
{
strcpy(subject,"n/a");
}
void getmarks()
{
cin>>marks;
}
double calgpa()
{
if(marks>=85 && marks<=100)
{
return gpa12=4.0;
}
else if (marks>=80 && marks<85)
{
return gpa12=3.7;
}
else if (marks>=75 && marks<80)
{
return gpa12=3.3;
}
else if (marks>=70 && marks<75)
{
return gpa12=3.0;
}
else if (marks>=65 && marks<70)
{
return gpa12=2.7;
}
else if (marks>=61 && marks<65)
{
return gpa12=2.3;
}
else if (marks>=58 && marks<61)
{
return gpa12=2.0;
}
else if (marks>=50 && marks<58)
{
return gpa12=1.0;
}
else if(marks<=0)
{
return gpa12=0;
}
}
void showgpa()
{
cout<<subject;cout<<" ",cout<<total;cout<<" ";
}
void add(gpa dld,gpa oop,gpa discrete,gpa comskills,gpa calcls,gpa stats)
{
float gpa12;
gpa12=(dld.gpa12*3+oop.gpa12*4+discrete.gpa12*3+comskills.gpa12*3+calcls.gpa12*3+stats.gpa12*3)/19.0;
cout<<" "<<"Result:"<<endl;
cout<<" "<<"GPA = "<<gpa12<<endl;
}
void percentage()
{
per=marks/100;
}
void grade()
{
if(marks>=85 && marks <=100)
cout<<"A+";
else if(marks>=80 && marks <85)
cout<<"A";
else if(marks>=75 && marks <80)
cout<<"B+";
else if(marks>=70 && marks <75)
cout<<"B";
else if(marks>=65 && marks <70)
cout<<"B-";
else if(marks>=61 && marks <65)
cout<<"C+";
else if(marks>=58 && marks <61)
cout<<"C";
else if(marks>=50 && marks <58)
cout<<"D";
else if(marks<50)
cout<<"F";
}
void presentation()
{
cout<<subject<<" "<<"100 "<<marks<<" "<<gpa12<<" ",grade(),cout<<endl;
}
void total1(gpa dld,gpa oop,gpa discrete,gpa comskills,gpa calcls,gpa stats)
{
int total1=(dld.marks+oop.marks+discrete.marks+comskills.marks+calcls.marks+stats.marks);
cout<<"Total 600 "<<total1<<" __ __ "<<endl;
}
};//endclass
int main()
{
gpa dld(100,0,0.0,"DLD "),oop(100,0,0.0,"OOP "),discrete(100,0,0.0,"Discrete Math "),comskills(100,0,0.0,"Comm Skills"),calcls(100,0,0.0,"Calculus 2 "),stats(100,0,0.0,"Statistics "),sum,total1;
cout<<"Enter your marks in following subject"<<endl;
cout<<"-------------------------------------------------------------------------------"<<endl;
cout<<"Subject Total marks Obtained marks"<<endl;
cout<<"------------------------------------------------------------------------------"<<endl;
dld.showgpa();dld.getmarks();
oop.showgpa();oop.getmarks();
discrete.showgpa();discrete.getmarks();
comskills.showgpa();comskills.getmarks();
calcls.showgpa();calcls.getmarks();
stats.showgpa();stats.getmarks();
cout<<"-------------------------------------------------------------------------------"<<endl;
dld.calgpa();
oop.calgpa();
discrete.calgpa();
comskills.calgpa();
calcls.calgpa();
stats.calgpa();
sum.add(dld,oop,discrete,comskills,calcls,stats);
cout<<" "<<"DETAIL:"<<endl;
cout<<"--------------------------------------------------------------------------------"<<endl;
cout<<"Subject T_marks O_marks GP Grade"<<endl;
cout<<"-------------------------------------------------------------------------------"<<endl;
dld.presentation();
oop.presentation();
discrete.presentation();
comskills.presentation();
calcls.presentation();
stats.presentation();
cout<<"--------------------------------------------------------------------------------";
total1.total1(dld,oop,discrete,comskills,calcls,stats); 
cout<<"--------------------------------------------------------------------------------";
cout<<endl<<endl<<"DEVELOPED BY : Programming passion tea"<<endl;
return 0;
}