# Why isn't my loop working?

4 views (last 30 days)
Madison Goodwin on 18 May 2018
Commented: Madison Goodwin on 18 May 2018
fid = uigetfile('*.*');
fid = fopen(fid);
deltat = 0.5;
n = 1;
while fgetl(fid)~= -1
line = fgetl(fid);
line = sscanf(line, '%f V, %i counts, %i ms');
vout = line(1);
counts = line(2);
t = line(3)/1000;
t(n+1) = t(n) + deltat;
% Q = flowrate (L/s)
% P = pressure
% p = density of water
p = 1000; %kg/m^3);
g = 9.81;
vs = 5;
% vout - get from data
% h - get from data
% Q - calculated from data
P = ((vout/vs) - 0.04)/0.0018;
h = (P/1000)/(p*g);
Q = counts/((t(n)/1000)*330);
% Finding hydraulic power
H =(Q*p*g*h)/1000;
end

Greg on 18 May 2018
Madison Goodwin on 18 May 2018
Ok now it is producing all the values, but the time step is not updating as I would like it, it is meant to increase by 0.5 seconds for each line, but for each line in the data the t value is 0.5.
Madison Goodwin on 18 May 2018
So if I have these two lines as my code will it update the timestep, the value of line(3) is 500ms. After dividing by 1000 it is 0.5, and deltat is 0.5
t = line(3)/1000;
t = t + deltat;

Greg on 18 May 2018
Edited: Greg on 18 May 2018
Purely a guess, you goofed up some indexing:
t = line(3)/1000; % <-- Recreates a new "t" as a scalar every loop iteration
t(n+1) = t(n) + deltat; % <-- Therefore, t(n) does not exist, or is 0
Also, I don't see you incrementing n anywhere.