Error in limiting user input to only numeric values?

Here is my code:

b = input('Enter the number of degrees celcius: ','s'); 
str2double(b); 

while (isnumeric(b) == false)
            disp(error_3)
            b = input('Enter the number of degrees celcius: ','s'); 
            str2double(b); 
end

I'm running into an error where it doesn't update b and check it again on each run of the while loop? How can I fix this?

Answer 1

[Walter Roberson]

str2double(b); 

That converts the character vector b into equivalent numeric form. Then it throws away the result because you did not assign it to anything.

while (isnumeric(b) == false)

The character vector is not numeric, and nothing you do inside your loop makes b numeric, so this is an infinite loop taking into account your other code.

If you were to have done b = str2double(b); then the result of that would always be numeric, and the isnumeric(b)==false would never succeed.

When b contains characters that are not valid in building a number, then str2double() returns nan. You can test for nan using isnan()

[Caleb Bell]

Thankyou! Works perfectly now