MATLAB: How to assign values to popup menu in GUI

matlab gui

I have a GUI to calculate the resistance of a resistor based on the number of bands and the color orders. I have 10 different colours, such as black, brown, red etc. I had tried to assign values to each color by using the following codes:
contents = cellstr(get(hObject,'string'));
popChoice = contents(get(hObject,'value'));
if strcmp(popChoice,'Black')
    popVal = 0;
elseif strcmp(popChoice,'Brown')
    popVal = 10;
elseif strcmp(popChoice,'Red')
    popVal = 20;
elseif strcmp(popChoice,'Orange')
    popVal = 30;
elseif strcmp(popChoice,'Yellow')
    popVal = 40;
elseif strcmp(popChoice,'Green')
    popVal = 50;
elseif strcmp(popChoice,'Blue')
    popVal = 60;
elseif strcmp(popChoice,'Violet')
    popVal = 70;
elseif strcmp(popChoice,'Grey')
    popVal = 80;
elseif strcmp(popChoice,'White')
    popVal = 90;
end
assignin('base','SecondColor',popVal)
The codes I used above actually works but all it does is saved the value into workspace and I have no idea how to use the value that's saved in the workspace to do calculation. Additionally, I had another function file that will do all the calculation based on the information gathered but I also have no clue on how to actually use it in GUI.Please help.
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