MATLAB: Countdown the received character

cell array

Hi guys, I have a function which will accept the characters and n, this function is a cell array with strings of decreasing lengths, from the integer n to 1. For example, when I type buildstr('a',4), the answer should be 'abcd' 'abc' 'ab' 'a'. However the code below doesnt satisfy my requirement. Can someone point out the error code?
function str=buildstr(ch,n)
  temp='';
  if(n<0)
      str='';
  else
      str=cell(n,1);
  for i=n:1
      if(i==1)
          str(i)={char(ch)};
      else
          temp=char(str(i+1));
       str(i)={strcat(temp,char(ch))};
      end
  end
  end

Best Answer

You’re almost there.
if(n<0)
    str='';
else
    str=cell(n,1);
    for i=n:-1:1
        if(i==n)
            str{i}=char(ch);
        else
            temp=char(str{i+1}+1);
            str{i}=strcat(char(ch),temp);
        end
    end
end
There were three problems:
  1. Your loop wasn’t iterating because in MATLAB, for loops by default count upward, so if the terminal value is less than the initial value, the loop is satisfied and never iterates. You need to decrement it by telling it to count down, specifying the interval to (in this instance) to be -1;
  2. Your ‘temp’ variable subscript needs to ‘look back’ (which is to say to add 1 to ‘i’) at every iteration, and add 1 to the previous value of ‘str’;
  3. Your strcat arguments were reversed.
A minor observation: it’s best to not use ‘i’ or ‘j’ as loop counters. They are the imaginary operators in MATLAB.
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