Why am I getting an unbalanced parenthesis error?

I am getting an error in line 8 of my code "if (~strcmp(a[:], ' '))" saying "Unbalanced or unexpected parenthesis or bracket." Why do I keep getting this error?

function [states, b] = Estimate_TransitionProbabilities(a)

n = length(a);
s = [];
b = [];
j = 0;
for i = 1:n
    if (~strcmp(a[:], ' '))
        s = (a, char(a(i)));

      elseif (-isempty(s))
          i = j+1;
          b(j) = s;
          s = [];
      end 
      if (i == n && -isempty(s))
          j = j+1;
          b(j) = s; 
      end 
  end

states(l) = b(l); l = 1;
for i = 2:length(l)
    num = 0
    for j = 1:i-1
        if (~strcmp(b(i),b(j)))
            num = num+1;
        end 
        if (num == i-1)
            l = l+1;
            state(l) = b(i)
        end
    end
end

num = zero(length(states), length(states))
for i = 1:length(states)
    for j = 1:length(states)
        for k = 1:length(i)
            if (strcmp(b(k), states(i)) & strcmp(b(k+1), states(i)))
                num(i,j) = num(i,j)+1
            end
        end
    end
end 
end

Answer 1

[Star Strider]

MATLAB uses parentheses ‘()’ not square brackets ‘[]’ for its subscript designations.

Try this:

if (~strcmp(a(:), ' '))

If ‘a’ is a cell array, this would be more appropriate:

    if (~strcmp(a{:}, ' '))

Note the curly brackets ‘{}’ for cell referencing.

It would help to know what ‘a’ is.