Question

Reuse the code to prompt the user for a specific day, test whether it is
within range, and then output the estimated concrete strength from the fitted
curve using polyval. Run your function from the command window for 2
different days to test the functioning of your code. The program should
preferably loop until the user asks to exit.

where

x = days

y = rain (mm)

x = [0 1 2 3 7 14 28];
y = [0 4 9.5 14 17.5 19.5 25.5];
%use polyfit to second order polynomial
a = polyfit(x,y,2);
xx = linspace(1,28);
yy = polyval(a,xx);

Answer 1

% Matlab script that prompts the user for a specific day, test whether it is
% within range, and then output the estimated concrete strength from the fitted
% curve using polyval.

x = [0 1 2 3 7 14 28]; % days
y = [0 4 9.5 14 17.5 19.5 25.5]; % rain (mm)

%use polyfit to second order polynomial
a = polyfit(x,y,2);
%xx = linspace(1,28);
%yy = polyval(a,xx);
done = false;

% loop that continues until the user exits
while ~done
% input the day
day = input('Enter a day(1-28): ');
  
% validate day to be between [1,28], re-prompt until valid
while day < 1 || day > 28
day = input('Day must be between [1,28]. Enter a day(1-28): ');
end
  
% calculate the concrete strength from the fitted curve using polyval.
rain = polyval(a, day);
  
% display the estimation
fprintf('The estimated concrete strength: %f\n',rain);
  
% ask if user wants to continue
contChoice = input('Enter "Y" to enter another day? ','s');
  
% if user wants to exit, set done to true
if strcmpi(contChoice,'y') == 0
done = true;
end
end

%end of script

Output: