switch statements and trig function

val = str2double(input('enter number','s')); 
chr = input('enter letter','s'); 
switch chr 
    case 's'
        disp(sin(val)) 
    case 'c' 
        disp(cos(val)); 
    case 't' 
        disp(tan(val));
    otherwise 
        disp('Oh no! Try a different character.'); 
end 

I wrote this code to find the sin,cos,or tan of an entered individual number. I now need to modify it so that instead of reading a single character/number, the program continually reads character/number pairs and displays the trigonometry result. If a number outside the range [-100, 100] is entered, the program should not display the trigonometry result and should ask for another character/number pair to be entered. I can't figure out how to make the initial modifications of reading in pairs - any shortcuts I can use?

[Kevin Phung]

what do you mean by reading in pairs?

[Marina Christakos]

instead of the program asking for a letter and number separately, I as the user am able to write c90 and the output will respond with 0

Answer 1

[Kevin Chng]

I think the most simple approach is to add another loop which is

val = str2double(input('enter number','s')); 
chr = input('enter letter','s'); 
if val>=-100 && val<=100
    switch chr 
        case 's'
            disp(sin(val)) 
        case 'c' 
            disp(cos(val)); 
        case 't' 
            disp(tan(val));
        otherwise 
            disp('Oh no! Try a different character.'); 
    end 
else
    warning('enter new input, your input is out of range')
end

[Marina Christakos]

that still makes me input the number and letter at separate times

[Kevin Chng]

I might miss understanding your question.

you may consider to use inputdlg, https://www.mathworks.com/help/matlab/ref/inputdlg.html

However, it is still input them in separate line, if wants to input in the same line, later, you might need to separate them since one is string/char and the other one is numeric

clc;clear all;

chr = input('enter letter & number :','s'); 
% Need some logic to separate them and ensure the user key in the right thing
C = {'1','2','3','4','5','6','7','8','9','0'};

for i = 1:10
Index = strfind(chr, C{i});
if isempty(Index)~=1
    if exist('thefirstdigit')==0
        thefirstdigit=Index;
    else    
        if thefirstdigit>Index
        thefirstdigit=Index;
        end
    end
end
end

%indexing to chr, then separate them into val and chr2
val = str2double(chr(thefirstdigit:end)); 
chr2 = (chr(1:thefirstdigit-1)); 
if val>=-100 && val<=100
    switch chr2 
        case 's'
            disp(sin(val)) 
        case 'c' 
            disp(cos(val)); 
        case 't' 
            disp(tan(val));
        otherwise 
            disp('Oh no! Try a different character.'); 
    end 
else
    

Run the program and enter :s100

Answer 2

[Kevin Phung]

you can just run the input once, and evaluate the input as a whole.

word = input('enter letter followed by number','s'); 
if numel(word)>1 
    chr = word(1);
    
    val =str2num(word(2:end))
    if isempty(val) || val >100 || val < -100 %occurs when 2nd character is a letter and not a number
        disp('Try again')
        return
    end
    
    switch chr 
        case 's'
            disp(sin(val)) 
        case 'c' 
            disp(cos(val)); 
        case 't' 
            disp(tan(val));
        otherwise 
            disp('Oh no! Try a different character.'); 
    end 
else
    disp('Try  again')
end