Simple MATLAB lexer program

I created a simple lexer program from MATLAB code where, when the user types a string, the lexemes in that string are categorized. However, when I enter a string in the command window only the first lexeme is getting displayed.

The code is as follows :

 function determineLexemes()
   prompt = 'Enter string : ';
   str = input(prompt);
   arr = char(str);
   j = 0;
   m = char(zeros(1,30));
   error = '';
   strTwo = '';
   display('Symbol Table');
   display('Lexeme \t\t Token');
   k = size(arr);
   for i = 1: k
  if(arr(i) == '+')
     display('+ \t\t ADD_OP');
  end
  if(arr(i) == '-')
     display('- \t\t SUB_OP');
  end
  if(arr(i) == '*')
     display('* \t\t MULT_OP');
  end
  if(arr(i) == '/')
     display('/ \t\t DIV_OP');
  end
  if(arr(i) == '(')
     display('( \t\t LEFT_PAREN ');
  end
  if(arr(i) == ')')
     display(') \t\t RIGHT_PAREN ');
  end
  if(arr(i) == '=')
     display('= \t\t EQUAL_OP ');
  end
  
  if(ischar(arr(i)) || isnumeric(arr(i)))
     strTwo = strTwo + arr(i);
  end
  if(~ischar(arr(i)) && ~isnumeric(arr(i)))
     if(~isspace(arr(i)) && ~isempty(strTwo))
            m(j) = strTwo;
            if(isNumeric(strTwo(1) && regexp('123abc', '^[A-Za-z0-9]+$')))
                disp(strcat('Error. Potential variable (', strTwo, ') whose name starts with digit found'));
                strTwo = '';
                j = j + 1;
            end
            if(~(isNumeric(strTwo(1) && regexp('123abc', '^[A-Za-z0-9]+$'))))
                disp(strcat(m(j), '\t\t' + 'IDENTIFIER'));
                strTwo = '';
                j = j + 1;  
            end 
        end
     end    
 end
end

And the intended output, when '(2a + b)' is entered to the user prompt,is as follows:

However the current output, when '(2a + b)' is entered to the user prompt, is as follows :

Any help on this problem is appreciated.

Answer 1

[Jos]

The function needs some work but couple of things that should help

- use fprintf instead of display

- replace k=size(arr) with k=length(arr)

- arr(i) is always a char so 'if(ischar(arr(i)) isnumeric(arr(i)))' will always be true

- for the same reason 'if(~ischar(arr(i)) && ~isnumeric(arr(i)))' is never true and everything below the statement cannot be reached

- the expression 'regexp('123abc', '^[A-Za-z0-9]+$')' does not contain any variables and is always true