I don't want a comma after the last number/value, how do i remove it (c++, loop)

Question

So, my friend's program is supposed to find the Multiplicative of Number three then print them out with a comma between the number. And not for the last one.

int a;
int b;

cout<< "First Number = ";
cin>>a;
cout<< "Last Number = ";
cin>>b;

if(a<=b)
{
    for(a;a<=b;a++)
    {
        if(a%3 == 0 && a%2 != 0)
        {   
            cout<<a;
        }
        if(a<b && a%3==0 && a%2 != 0)
        {
            cout<< " , ";
        }
        else if(a==b)
        {
            cout<< ".";
        }
    }
}

And after i input

a = 1

b = 20

this is what i expected

3 , 9 , 15.

and this is what i actually get

3 , 9 , 15 , .

Answer 1

I would do something like this:

char const* sep = ""; // item separator (nothing to begin with)

for(a;a<=b;a++)
{
    if(a%3 == 0 && a%2 != 0)
    {   
        cout << sep << a; // output the separator before the next value
        sep = ", "; // now change it to a comma
    }
}

cout << "."; // finish with a full stop