Terminate while loop when user hits enter

Hi eveyone,

This is my while loop. It must end when user hits enter without entering a value . The loop allows for upto 3 successive blank entries before terminating. And, I cant get the n_points matrix to save entries without error.

How do I fix these?

Thank you for your time.

clear all
disp('Begin entering the data points')
t = 1;
x_point = input('enter x : ') 
y_point = input('enter y : ')
n_points = [x_point,y_point];

while x_point ~= isempty(x_point) | y_point ~= isempty(y_point) % does not terminate immedeately when user presses enter without entering a value. 
    x_point =  input('enter x : ')
    y_point =  input('enter y : ')
    t = t+1
    n_points(t,:) = [x_point,y_point];  
end

Answer 1

[Jan]

Avoid repeating code:

disp('Begin entering the data points')
t = 0;
while true     % Infinite loop
    x_point = input('enter x : ');
    if isempty(x_point)
       break;  % Stop the WHILE loop
    end
    y_point = input('enter y : ');
    if isempty(y_point)
       break;  % Stop the WHILE loop
    end
    t = t + 1;
    n_points(t, :) = [x_point, y_point];  
end

Or:

disp('Begin entering the data points')
t     = 0;
ready = false;
while ~ready
    x_point = input('enter x : ');
    if ~isempty(x_point)
       y_point = input('enter y : ');
    end
    
    if ~isempty(x_point) && ~isempty(y_point)
       t = t + 1;
       n_points(t, :) = [x_point, y_point];
    else
        ready = true;
    end
end

[klb]

Thanks Jan, this works. Much aprpeciate the two different while loop logics. With these, you have clarified the following as well.

For some reason I have been under the impresison that the loop terminating logic must only be provided at the start of loop, and statements in the loop run till that logic returns a false. I see now that a while loop can be terminated from inside the loop as well. Thank you!

Answer 2

[Jonathan Clayton]

the code below looks at the number of elements that the user has inputed for that loop, and if that number is zero then the loop is broken.

if numel(x_point)+numel(y_point)==0
        break
end

Add this code above n_points variable so that the empty vaibles are not added to your list.

[klb]

The logic for your answer code inherently allows for user to hit enter upto two times at least without entering any values, before terminating the While loop. It also allows user to skip entering a data point. My main query, as indicated by the question title is:

While loop needs to terminate at the very first time user hits enter without having adding data.

[Jonathan Clayton]

ok so that is a simple fix

if numel(x_point)==0
        break
end

add this if statement directly after where the user adds the x_point in the while loop. this will break the loop if the user does not input anything when promted and simply hits enter.

[klb]

Incorporated your code block as seen in code below. If you run it, skipping x is ok. But skipping y value copies the x value to y. If I add your code a second time with if numel(y_points)==0 edit, It works , but that is blunt.

A while loop shouldnt need further fixes. That is my original question - how to terminate the While loop at the very first time user hits enter without having adding data.

clear all
disp('Begin entering the data points')
t = 1;
x_point = input('enter x : ') 
y_point = input('enter y : ')
n_points = [x_point,y_point];

while x_point ~= isempty(x_point) | y_point ~= isempty(y_point)
    x_point =  input('enter x : ')
    y_point =  input('enter y : ')
   
    if numel(x_point)==0
        break
    end
    
    t = t+1
    n_points(t,:) = [x_point,y_point];  
end

I tried another logic here but it also needs 2 of those code blocks. Cant understand why doesnt the loop break with the main while loop conditon itself. Any suggestions to eliminate in-loop intemedeate conditions checks?

clear all
t=0;
x_point = 0;
y_point = 0;

while numel(x_point)~= 0
    x_point =  input('enter x : ')
    y_point =  input('enter y : ')
    
   if numel(x_point)==0
        break
   end
   if numel(y_point)==0
        break
    end
    
    t = t+1;
    n_points(t,:) = [x_point,y_point]
end
    n_points
    

[klb]

Jonathan, I am using the code block. I am also learning its ok to terminate a while loop from the inside the loop. Thanks for your time and help!