I am trying to run a while loop for simulation of test on the computer and it stops at the second if loop stating that it is busy

clear all
close all
clc

Letters=[]

while j<9
if j<1
i = 'E';
set (figure, 'color', [1 1 1])
figure(1)
clf,text(.45, .6, 'E', 'fontname', 'Times', 'fontsize', 200)
axis off
pause
LetterOne = input('What letter did you see on the screen?', 's')
LetterOne = upper(LetterOne)
if char(i)  == char(LetterOne)
    disp('Press a key to continue')
else disp('Thank you participating in the vision test.')
    disp('Your vision is 20/200');
   return
end
end

if j<2
i= 'F P';
set (figure, 'color', [1 1 1])
figure(2)
clf,text(.40, .6, 'F P', 'fontname', 'Times', 'fontsize', 100)
axis off
pause
LetterTwo = input('What letter did you see on the screen?', 's')
LetterTwo = upper(LetterTwo)
if char(i)  == char(LetterTwo)
    disp('Press a key to continue')
else disp('Thank you participating in the vision test.')
    disp('Your vision is 20/100')
    return
end
 end

if j<3
i = 'T O Z';
set (figure, 'color', [1 1 1])
figure(3)
clf,text(.35, .6, 'T O Z', 'fontname', 'Times', 'fontsize', 70)
axis off;
pause
LetterThree = input('What letter did you see on the screen?', 's')
LetterThree = upper(LetterThree)
if char(i)== char(LetterThree)
    disp('Press a key to continue')
else disp('Thank you participating in the vision test.')
    disp('Your vision is 20/70');
    return
end
clf
end
end

Individually the code runs in sections but not as a whole

Answer 1

[Image Analyst]

When you do

if char(i)  == char(LetterOne)

the badly-named "i" is already a character so there is no need to cast it to char. Next, don't compare strings like that. Use strcmpi() instead. Third, use isempty() to check if the user simply hit enter instead of characters and take appropriate action (warn them, or exit, or whatever). Fourth, you should remove white space in case users put spaces between the letters:

if ~isempty(LetterTwo)
    LetterTwo(LetterTwo == ' ') = []; % Remove spaces.

So keep at it. Try those things and let us know if you have any further problems.

Answer 2

[NAMRATA SINGH]

Thank you for your reply image analyst. I am confused on how to address your third suggestion- 'Third, use isempty() to check if the user simply hit enter instead of characters and take appropriate action (warn them, or exit, or whatever).' How can I do it in the if statement?

Thank you, Namrata