While Loop regarding user input type stuck on infinite else loop

I need to check user input to make sure it's a number. The first part of the while loop works if i input a number, but the 'else' part gets stuck on infinite loop if I input something else, and it won't go out even if I input a number.

%Part of a Program to calculate equivalent resistance for series and parallel circuits

n = input('Enter Number of resistors: ')


for count = 1:n  
    %input resistance values into an array
    R(count) = input(['Enter the value of Resistor ' num2str(count) ': ']); 
    flag = false; 

     while ~flag 
          num = isnumeric(R(count));    %check if resistance input is a number

          if num == true  %This part works and i can get through the whole for loop if I enter numbers correctly
               flag = true;
    
          else  %This part gets stuck on an infinite loop even if I enter a number
               disp('incorrect entry');
               R(count) = input(['Enter the value of Resistor ' num2str(count) ': ']);   
   
end 
end   
end

[Rik]

What input are you trying? I don't get any infite loop on R2020a.

For readability, you should use the smart indent (in most releases you can select your code and hit ctrl+i), and remove empty lines that don't divide distinct parts of your code. You should also pre-allocate R and write some comments in your code that describe the flow of your program.

[Shadi Khansa]

I edited the code to make it more readable. The for loop works as long as I input numbers, but if I input a character or string, then it gets stuck infinitely on the 'else' part even if I enter a number.

Answer 1

[Rik]

The data type of R is not changing, so if you create it as a char, it will never be numeric. If you want to use this setup, you need to use a cell array instead. Another method is to use a temporary variable and store that in R once it is valid:

n = input('Enter Number of resistors: ');
R=zeros(1,n);
for count = 1:n
    tmp=NaN;%enter loop
    while isnan(tmp)
        tmp = input(['Enter the value of Resistor ' num2str(count) ': '],'s');
        tmp=str2double(tmp);
    end
    R(count)=tmp;
end

[Shadi Khansa]

Thank you!