While[xop[[i]] > xq, 
          xop = Append[xop, yop[[i]]/(\[Alpha]m + (1 - \[Alpha]m)*yop[[i]])]; 
          yop = Append[yop, R/(R + 1)*xop[[i + 1]] + xd/(R + 1)]; 
          pv[[i]] = 
           Graphics[
            Line[{{xop[[i + 1]], yop[[i]]}, {xop[[i + 1]], yop[[i + 1]]}}]];
          ph[[i]] = 
           Graphics[Line[{{xop[[i]], yop[[i]]}, {xop[[i + 1]], yop[[i]]}}]]; 
          n = i; i++];

Hello, I'm creating a function for McCabe-Thiel method. I want to use Graphics in While loop to store plots in list. But I can't save it on the list. I'd like to know if there is another way. (English may be a little awkward because I am not from America.)

To give you an easier example:

pr = {}; i = 1; While[i > 4, 
 pr = AppendTo[pr, Graphics[Line[{{i, i}, {i + 1, i + 1}}]]]]

result : pr={}

Why???