ANSWER: How to check if you wrote string or number

Hi there, this might help you out. I made a short code that takes in a number (or string) from a user and returns the number if it sure is a number or 0 if it's a string.

copy and paste in a "script" to try out. Save the script and then test it in comand window.

number = input('Type a number please =  ', 's'); 
% this pice of code can take in both numbers or strings:

number = str2num(number); 
%If the string "number" does not represent a valid number or matrix,
    str2num(number) returns the empty matrix. 

if  isempty(number)
   answer = 0;
else
   answer = daysInMonth(number);
end

disp(answer)

or:

number = input('Type a number please =  ', 's'); 
number = str2num(number); 

if  isempty(number)
 disp('You wrote a text')
else
   fprintf(' You wrote the number %2.0f\n ', number)
end

I know this might be a problem for lots of people which they need an answer to. Lets hope it helps

BenDyAsk

[Walter Roberson]

This code does not really do what it is designed for. Consider

str2num('system(''ls'')')

which you will find executes the ls command instead of just detecting that the string is not a number.

str2num() uses eval() on the string you provide.

[Benjamin Askelund]

Hi Walter, It works just as intended.. I suggest that you try it out and see.

number = input('Type a number please =  ', 's'); 
number = str2num(number); 

if  isempty(number)
 disp('You wrote a text')
else
   fprintf(' You wrote the number %2.0f\n ', number)
end

It works perfectly fine for me

[Benjamin Askelund]

This is ofc for beginners in MATLAB. As tehere is not easy for them to find something that fit to there lvl of programming skils. Its a short code to analyze

[Walter Roberson]

>> number = input('Type a number please =  ', 's'); 
number = str2num(number); 

Type a number please =  system('ls')
Add-Ons      SupportPackages    projects
Examples    power_V2G_acc.mexmaci64  slprj

You are taking whatever string the user provides and you are executing it.

str2num is coded as very nearly literally

result = eval( [ '[' TheInputString ']' );

so if the user inputs a string that is a valid function call, the function will be executed.

Another example:

>> number = input('Type a number please =  ', 's'); 
  number = str2num(number); 
Type a number please =  pi
>> number
number =
          3.14159265358979

How did number get that numeric value when the user entered something that contains no numbers? Answer: because pi is actually a function, and the function was called.

Is this working "as intended" ??

[Stephen23]

Running str2num does not do what the OP thinks, and actually executes the input string. It does not test for string vs. number:

>> str2num('i')
ans =  0 + 1i
>> str2num('exp(3)')
ans =  20.086
>> str2num('mean(+''cheese'')')
ans =  103.50

A much better choice would be str2double.

I am going to close this question because it is misleading, and gives wrong information.