Program on Milk man problem

A Milkman serves milk in packaged bottles of varied sizes. The possible size of the bottles are {1, 5, 7 and 10} litres.
He wants to supply desired quantity using as less bottles as possible irrespective of the size. Your objective is to help him find the minimum number of bottles required to supply the given demand of milk.


#include <iostream.h>
#include<conio.h>
int left(int,int);
int min(int,int);
void main()
{
int N,Demand,litres,L,L10,L7,L5; //N=cases check
clrscr();
cout<<"Enter the number of Cases\n ";
cin>>N;
for(int i=0;i<N;i++){
 cout<<"Enter the litres of Milk:\n ";
cin>> Demand;

int const required=Demand;
//for 10 litres
litres= Demand/10;
L=litres;
litres*=10;
Demand-=litres;
L10=left(Demand,L);

//for 7 litres
Demand=required; //reset demand
litres= Demand/7;
L=litres;
litres*=7;
Demand-=litres;
L7=left(Demand,L);

//for 5 litres

Demand=required; //reset demand
litres= Demand/5;
L=litres;
litres*=5;
Demand-=litres;
L5=left(Demand,L);


cout<<min(L5,min(L10,L7))<<" Bottles required n\n";
}


}

int left(int Demand,int L)
{
 int left;
switch (Demand){
case 0: left=0;
 break;
case 1: left=1;
 break;
case 2: left=2;
 break;
case 3: left=3;
 break;
case 4: left=4;
 break;
case 5: left=1;
 break;
case 6: left=2;
 break;
case 7: left=1;
 break;
case 8: left=2;
 break;
case 9: left=3;
 break;
}
L+=left;
return L;
}

int min(int a,int b){
if (a<b)
return a;
else
return b;
}