Function to encoding input characters in MATLAB - arrays

Question

I want to create a function that encrypts the input sentence. This encryption will replace the first letter of each word with the next letter in the ASCII table, and the second letter with the next, ....
So basically, the resulting output for abc def should be bcd efg. However, when I run my function, the space will also be replaced, i.e. output will be bcd!efg. Why is this so? Thanks.
Below is what I have written:
function out = encrypt(input)
ascii_encode=double(input);
line={ascii_encode};
counter=0;
for a=1:length(line)
if line{a}==32
counter=0;
else
counter=counter+1;
line{a}=line{a}+counter;
end
line{a}=char(line{a});
end
out=line;
end

Answer 1

You should be careful handling cells.
Try line{a} , line(a) , line(1){a}, to understand how they work.
The code should be like this,
function out = encrypt(input)
ascii_encode = double(input);
line = {ascii_encode};
for a = 1 : length(line{1})
if line{1}(a) == 32
continue;
end
line{1}(a) = line{1}(a) + 1;
end
line{1} = char(line{1});
out = line{1};
end
And there is no need for counter, you just have to jump when if is true.

Answer 2

Kamtal's answer is perfectly right. You assign your input to a cell and then you were not accessing an index in the cell value (which is still a char array), but the full cell value.
Follow Kamtal answer if you still want to use cells type, and look at the cell documentation.
Note that you could also benefit by Matlab vectorization capabilities, and simplify your function by:
function out = encrypt(input)
charToKeep = ( input==' ' ) ; %// save position of character to keep
out = char(input+1) ; %// apply the modification on the full string
out(charToKeep) = ' ' ; %// replace the character we saved in their initial position
end