CALCULATOR BY C++

#include<iostream.h>
#include<conio.h>
int sum();
int sub();
int mul();
void main()
{
clrscr();
int d,ch;
cout<<"menu   \n";
cout<<"1 add\n"<<"2  sub\n"<<"3 mul\n";
cout<<"enter your choice\n";
cin>>ch;
switch(ch)
{
case 1:d=sum();
break;
case 2:d=sub();
break;
case 3:d=mul();
break;
default:
cout<<"wrong choice";
}
cout<<d;
getch();
}
int sum()
{   int a,b,c;
cout<<"enter two values";
cin>>a>>b;
c=a+b;
return c;
}
int sub()
{
 int a,b,c;
cout<<"enter two values";
cin>>a>>b;
c=a-b;
return c;
}

int mul()
{   int a,b,c;
cout<<"enter two values";
cin>>a>>b;
c=a*b;
return c;
}