Vector isn't storing the values passed to it?

I am going to ask a user to give me positive numbers, and I will quit once the user enters a negative number. Then, I will display all the positive numbers that they had entered. The code reads find to me, but for some reason, the array is not putting in the first positive number that the user passes to it... Any ideas will be greatly appreciated. Thank you.

i=0;
answer='Enter a positive number: ';
x=input(answer);
while x>0
    x=input(answer);
    i=i+1;
    A(i)=x;
end

Answer 1

[Stephen23]

pmt = 'Enter a positive number: ';
num = str2double(input(pmt,'s'));
vec = [];
while num>0
    vec = [vec,num];
    num = str2double(input(pmt,'s'));
end

And tested:

Enter a positive number: 5
Enter a positive number: 3
Enter a positive number: 1
Enter a positive number: -1
>> vec
vec =
   5   3   1

Note that I used the 's' option and wrapped input in str2double, which avoids the unnecessary risk of the user inputting arbitrary code (which would then be executed by input) or unsuitable values.

[Ame Michael]

Hello Stephen,

thank you so much for your help. Can you please tell me, what does the 's' option do? I removed it so see it's role in the script, leading to the script not running. Just curious, correct me if I am wrong, do I always use the 's' in conjunction with the str2double function?

Thank you very much.

[Stephen23]

@Ame Michael: the 's' option is explained in the input help, which I am sure that you have read, so you will know that it makes input return the exact char vector that the user has entered, otherwise the input will be evaluated and the first output returned: experienced MATLAB users consider evaluating any arbitrary input to be insecure and a bad practice. At the very least it can lead to unpredictable errors unless you add a lot of checks on what was returned by input (e.g. array class and size). It is a lot simpler to use the 's' option and str2double, which always returns a scalar numeric (which is NaN if the input was not a valid number).