MATLAB: How to convert grade into letter grade

MATLAB

Hi guys, wonder how to transfer grade into letter grade. I have already calculated the code, which is following:
NA = 4;
PS = [75, 62, 80, 71, 0, 32, 56, 80];
PR = 68;
EM = 78;
n=2;
u=unique(PS)
if numel(u)==1 || numel(u)==2
    Result=[]
else
    Result=mean(PS(~ismember(PS,u(1:n))))
end
a = Result
if NA <= 2
    b = 15
end
if NA == 3
    b = 14
end
if NA == 4
    b = 13
end
if NA == 5
    b = 12
end
if NA == 6
    b = 11
end
if NA == 7
    b = 10
end
if NA == 8
    b = 9
end
if NA == 9
    b = 8
end
if NA == 10
    b = 7
end
if NA == 11
    b = 6
end
if NA == 12
    b = 5
end
c = PR*0.3
d = EM*0.2
e = a*0.35
grade = b + c + d + e
NA = 1;
PS = [90, 100, 100, 84, 89, 92, 73];
PR = 96;
EM = 0;
n=2; % two smallest values
u=unique(PS)
if numel(u)==1 || numel(u)==2
    Result=[]
else
    Result=mean(PS(~ismember(PS,u(1:n))))
end
a = Result
if NA <= 2
    b = 15
end
if NA == 3
    b = 14
end
if NA == 4
    b = 13
end
if NA == 5
    b = 12
end
if NA == 6
    b = 11
end
if NA == 7
    b = 10
end
if NA == 8
    b = 9
end
if NA == 9
    b = 8
end
if NA == 10
    b = 7
end
if NA == 11
    b = 6
end
if NA == 12
    b = 5
end
c = PR*0.3
d = EM*0.2
e = a*0.35
grade = b + c + d + e
I know I am super unskilled lol. Anyway, at first I tried
function grade=letter_grade
    if grade >= 91
        letter_grade='A';
    elseif n >= 81
        letter_grade='B';
    elseif n >= 71
        letter_grade='C';
    elseif n >= 61
        letter_grade='D';
    else
        letter_grade='F';
    end
end
but it doesn't work. Please help me with that, thanks in advance.
PS: 90-100 A+
       80-89  A
      70- 79 B
       60-69 C
       50-59 D
      below 50 F

Best Answer

I guess this is what you intended
function  grade = letter_grade( n )
    if n >= 91
        grade='A';
    elseif n >= 81
        grade='B';
    elseif n >= 71
        grade='C';
    elseif n >= 61
        grade='D';
    else
        grade='F';
    end
end
and test the function 
>> letter_grade( 75 )
which returns "C"
However, note that this function will not give results according to 
PS: 90-100 A+
       80-89  A
      70- 79 B
       60-69 C
       50-59 D
      below 50 F
but it runs without errors.
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