While loop not working (beginner)

I am trying to count how "long" the array for k_earth is and assign it a variable. height_earth is an array. I need to use some kind of for or while loop. When I run this code:

k_earth = find(height_earth >= 0); % Values where the ball is in the air

while height_earth>= 0

L = length(k_earth);

end

I get the error :

Unrecognized function or variable 'L'.

Error in EGR_115_Final_Project_Hall_Alexis (line 62)

time_impact_earth = time(k) ; % Time when ball impacts

and if I put in a value for L, it does not change after running through the for loop.

[David]

Hi! Did you try to assingn 'L' with a default value (Like 1) from out of the loop?

Answer 1

[Vinayak Choyyan]

Hi Alexis

I have not quite understood what you are trying to achieve.

In your code,

height_earth

is an array and height_earth>=0 will result in a logical array. For example if

height_earth= [1 2 3 4 5 -1 -2 -3]; %then
height_earth>=0 %results in [1 1 1 1 1 0 0 0]

You have written while height_earth>=0. While needs an expression that will result in a single logical value, that is, result to true or false, but you are giving it an array. The code doesn’t enter the while loop and hence the value of L remains unchanged.