gui matlab gpa calculator

Hi guys

I'm trying to learn about GUDIE and GUI really tried youtube but can't grasp alot of things

here I have GPA caluclator

GPA = total grade points / total hours

I made it to total hours but really can't make it run , how do I assaign popmenue to meaingful values ? tried this way

A=4

B=3

C=2

D=1

F=0

but didn't work

attached my files but main code i did is

x1= str2double(get(handles.c1,'string'));
x2= str2double(get(handles.c2,'string'));
x3= str2double(get(handles.c3,'string'));
x4= str2double(get(handles.c4,'string'));
x5= str2double(get(handles.c5,'string'));
x6= str2double(get(handles.c6,'string'));
x7= str2double(get(handles.c7,'string'));
totH= x1+x2+x3+x4+x5+x6+x7
set(handles.totH,'string',totH);


A=4
B=3
C=2
D=1
F=0
GP1=c1*g1
GP2=c2*g2
GP3=c3*g3
GP4=c4*g4
GP5=c5*g5
GP6=c6*g6
GP7=c7*g7
gpa= GP1+GP2+GP3+GP4+GP5+GP6+GP7/totH
set(handles.gpa,'string',gpa);

thanks