How to change ASCII values?

Question

Kyle Donk 2020-1-25

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https://ww2.mathworks.cn/matlabcentral/answers/501955-how-to-change-ascii-values

评论： Star Strider 2020-1-25

I have an assignment where I have to take a phrase, capitalize it, and use the 'double' command to change all of the letters to uppercase. I'm then supposed to loop through the resulting array of letters and change the ASCII values to values like: A=0 B=1 C=2, etc. The problem is that I've tried nearly everything to do that, but so far nothing is working. I was hoping that someone could point out what I am doing wrong and point me in the right direction. Thanks!

Here is what I have so far:

function y=stringcode(k)
k=('Zoinks!')
upper('Zoinks!')
y=double('Zoinks!')
for i=1:length(k)
    A=0;
    B=1;
    C=2;
    D=3;
    E=4;
    F=5;
    G=6;
    H=7;
    I=8;
    J=9;
    K=10;
    L=11;
    M=12;
    N=13;
    O=14;
    P=15;
    Q=16;
    R=17;
    S=18;
    T=19;
    U=20;
    V=21;
    W=22;
    X=23;
    Y=24;
    Z=25;
end
end

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Answer 1

Star Strider 2020-1-25

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You are not using tthe result of the upper call.

See if:

u = upper(k)
y = double(u)

is more appropriate.

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Walter Roberson 2020-1-25

for i=1:length(k)
    if k(i) == double('A')
        output(i) = 0;
    elseif k(i) == double('B')
        output(i) = 1;
    elseif k(i) == double('C')
        output(i) = 2;
    all the way to 'Z'    
    end
end

Star Strider 2020-1-25

‘I'm then supposed to loop through the resulting array of letters and change the ASCII values to values like: A=0 B=1 C=2, etc.’

If you want to replace the elements of ‘y’ by their equivalents in the ‘A=0 B=1 C=2, etc.’ relation you created, you need to compare each one with the alphabetical elements of the relation. Then replace it with the respective value from the numeric equivalent. (There are more efficient ways to do this, however you are apparently supposed to loop through them, so I leave that to you.)

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Answer 2

Allen 2020-1-25

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I simple way of converting characters values or character vectors to apply a numerical calculation directly to the characters.

k = 'Zoinks!';
y = upper(k)-0; % ASCII values for the uppercase versions of all characters. This includes "!" as well.
% Same as k = str2double(upper(k));

Since the ASCII value of A is 65, if you want to shift the values that are returned such that A = 0 you can do this at the same time you convert to ASCII values.

y = upper(k)-65; % Shifts ASCII values at the same time as converted so that A = 0;

If you need to remove punctuation from the characters you can use regular expressions to do this.

% Replaces anything that is not A-Z with an empty string (including whitespace characters) and converts
% to shifted ASCII values.
y = regexprep(upper(k),'[^A-Z]','')-65;

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Kyle Donk 2020-1-25

Ok. My college does have an honor code, so I will abide by that. I have to loop through this array to find the answer anyway, so Allen's solution might not have even helped.

What frustrates me is that the project that I am working on is not hard but I am struggling so bad in this course. I don't have a programming background (this is my first programming course), but other students seem to be learning this material so much more easily. (Rant over :) )