When I set the voltage = 2.5, the volume isn't being calculated and displayed on the command window and the wrong value for US Gallons is being calculated. Everything else is working apart from this

%code to calculate volume of water in a cylinder tank 
voltage = 2.5; %input voltage from floater   

%tank dimensions
A = 2.63;
B = 3.945;
C = 5.9175; 
D = 1.9725; %this value is B/2 

%minimum_voltage = acosd(B/2*A)*5/180;
minimum_voltage = 1.15;
%maximum_voltage = ((180 - minimum_angle)/180)*5;
maximum_voltage = 3.85; 
fprintf('Min voltage = %f.  Max voltage = %f.\n', minimum_voltage, maximum_voltage);

%Convert voltage to angle
%minimum_angle = 180 - angle at minimum_voltage 
angle = (voltage*180)/5;
 fprintf('angle = %f.', angle);

%Check input voltage is valid 
if voltage < minimum_voltage 
    disp('ERROR - check the floater') 
elseif voltage > maximum_voltage 
    disp('ERROR - check the floater')
else
    disp('Voltage seems sensible') 
end 
    
%Calculate correct water levels (volume)
if voltage == 1.15
    disp('tank is empty')
    %tank is empty
end

if voltage == 2.5
    %tank is half full
    tank_depth = D;
    disp('tank is half full')
     fprintf('tank depth = %f.', tank_depth);
end 

if voltage == 3.85
    disp('tank is full')
    %tank is full
end 

%Volume of the tank
if voltage == 1.15
    volume = 0;
    fprintf('Volume = %f.', volume);
end

if volume == 2.5
    volume = (pi*((D)^2)*C)/2;
     fprintf('Volume = %f.', volume);
end

if voltage == 3.85
    volume = pi*((D)^2)*C;
    fprintf('Volume = %f.', volume);
end

%Conversion to US gallons 
US_gallon = 264.172*volume;
 fprintf('US gallon = %f.', US_gallon);

 
>>VolumeCalculations
Min voltage = 1.150000.  Max voltage = 3.850000.
angle = 90.000000.Voltage seems sensible
tank is half full
tank depth = 1.972500.US gallon = 19107.723459.

Answer 1

[DGM]

This should fix the one error:

if voltage == 2.5 % voltage, not volume
    volume = (pi*((D)^2)*C)/2;
     fprintf('Volume = %f.', volume);
end
if voltage == 3.85
    volume = pi*((D)^2)*C;
    fprintf('Volume = %f.', volume);
end

For any practical application, you might want to avoid strict equality tests on floating-point inputs. If this is homework and the tests are working, then robustness doesn't really matter.

Regarding volume calculation, nobody can guess what the problem definition is. Nobody knows what dimensions A,B,C,D mean for a cylinder or what units they're in. Nobody knows where the sensor is mounted or what its range is or how that translates into physical units. You'll have to debug that.

[Stephen23]

"you might want to avoid strict equality tests on floating-point inputs."

Not "might want to", but have to (because otherwise the code is latent buggy, and will just fail later).

"If this is homework and the tests are working, then robustness doesn't really matter."

Latent bugs due to poor floating point handling are often not picked up by a few hand-picked values.

Much better: show the OP exactly why they need to learn how to handle floating point. Replace equality with:

abs(A-B)<tol