You need to give r a value to manipulate it, even if it is just 0. I assume you accidentally put cin>>c; beside rows instead of cin>>r;. You are also missing braces for your else statement.
//begin
#include <iostream>
using namespace std;
int main()
{
unsigned int r,c;
cout<<"rows:" ; cin>>r; //this was cin>>c before
cout<<"colimns:" ; cin>>c;
if(r<c)
cout<<"A: ("<<r<<";"<<r<<")"<<endl
<<"B:"<<r<<endl
<<"V:"<<(r-1)*r/2+r*(c-r)<<endl;
else
{
cout<<"A:("<<c<<","<<c<<")"<<endl
<<"B:"<<c<<endl
<<"V:"<<(c-1)*c/2<<endl;
}
return 0;
}
//end
P.S This is some of the messiest code i have ever seen