WindowResizing with ofxSimpleGuiToo (ComboBox)

I try to set up 3 predefined window sizes that could be changed by clicking one from a drop down menu list. I use memo’s ofxSimpleGuiToo / gui.addComboBox for the drop down GUI list.

string titleArray[] = {"640x480", "800x600", "1024x768"};
gui.addComboBox("Screen size (4:3)", winNewSize, 3, titleArray);

and something along the lines of:

void ofApp::windowResized(int w, int h){
    ofSetWindowShape(w, h);   

for modifying the window size.

I can’t figure out how to assign 3 sets of values for each of the 3 titles, to be used by the “w” and “h” variables. Or how (my) “winNewSize” variable actually work with the 3 titles.

Any hints and tips are highly appreciable.
Thank you.

Any advice on this? I am still trying to figure this out.
I tried something like this but without luck…

void ofApp::windowResized(int w, int h){
    if(winNewSize == 2) {
        ofSetWindowShape(800, 600);

Thank you