MATLAB: How to replace char in array with a double

char to doublereplacement

I am making a program that converts Roman numerals to numerical values. My current code is below.
%%Roman Numeral Conversion
%Declare variables
I=1;
V=5;
X=10;
L=50;
C=100;
D=500;
M=1000;
%input Roman numeral
Roman=input('Roman numeral: ','s')
letters=cellstr(Roman')'
for n=1:length(letters)
    if (strcmp(letters(n),'I'))||(strcmp(letters(n),'i'))
        letters(n)=1;
    elseif (strcmp(letters(n),'V'))||(strcmp(letters(n),'v'))
        letters(n)=5;
    elseif (strcmp(letters(n),'X'))||(strcmp(letters(n),'x'))
        letters(n)=10;
    elseif (strcmp(letters(n),'L'))||(strcmp(letters(n),'l'))
        letters(n)=50;
    elseif (strcmp(letters(n),'C'))||(strcmp(letters(n),'c'))
        letters(n)=100;
    elseif (strcmp(letters(n),'D'))||(strcmp(letters(n),'d'))
        letters(n)=500;
    elseif (strcmp(letters(n),'M'))||(strcmp(letters(n),'m'))
        letters(n)=1000;
    else disp('Not valid entries')
        break
    end
end
number=sum(letters)
text=sprintf(Roman,'= %d',number)
disp(text)
When I run this, I get the error below when I try to substitute the letter for its corresponding numerical value.
Conversion to cell from double is not possible.
Error in Roman_Numeral_Conversion (line 21)
        letters(n)=10;
How can I avoid this problem?

Best Answer

You made a cell array with this line:
letters = cellstr(Roman')'
That is why you are getting the conversion error. Make it a double instead. E.g.,
letters = zeros(size(Roman));
Then in your loop, compare with Roman instead of letters. E.g.,
    if (strcmp(Roman(n),'I'))||(strcmp(Roman(n),'i'))
        letters(n)=1;
    elseif (strcmp(Roman(n),'V'))||(strcmp(Roman(n),'v'))
        letters(n)=5;
            :
           etc
However, this is just a character conversion code. You still need to put in logic for when values are added vs subtracted. E.g., your code will give an answer of 11 for 'XI' as well as 'IX' when the latter should be 9.
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