Mass of a prism using a 'While loop'

I copied the solution I wrote as a comment here as an answer:

First of all, your calculation is wrong: mass = density * volume

As far as I understood the question, you should calculate the mass of a rectangular prism with a hole (cylinder) in it. To get the total mass you have to subtract the mass of the hole from the mass of the massive rectangular prism.

Although I have to admit, that the given task is very bad! It mixes diameter and radius of a hole/cylinder and the parameter for the height of the rectangular prism is missing.

If I assume, that it's the diameter, that is meant by "(r=0.05:0.1:<W/2)" and not the radius, and height = width (quadratic) for the prism, than the following code should do the trick:

% mass of rectangular prism with a hole (cylinder) in it
clear, clc
rho = 2700;

W = 1;              % Width of rectangular prism
L = 2;              % Length of rectangular prism
d0 = 0.05;          % Initial diameter of the hole (cylinder)
dStepwidth = 0.1;   % Stepwidth of the diameter of the hole
dMax = W/2;         % Maximum diameter of the hole

for d = d0 : dStepwidth : dMax
    mass_prism = W^2 * L * rho;
    mass_hole = (pi * (d/2).^2 * L) * rho;
    mass_total = mass_prism - mass_hole;
    printf ( 'd = %0.3f m \nW = %0.1f m \nL = %0.1f m \nRho = %0.3f kg/m^3 \nm = %0.5f kg\n\n',...
        d, W, L, rho, mass_total);
end 

Converting a for-loop into a while-loop is simple, you just do, what the for-loop does by hand:

1. create a variable d outside of the loop and initialize it with the starting value d0

2. think about the condition, when the while-loop should stop or continue to run. In your case this is d <= dMax. The loop continues as long as d is lower or equal dMax.

3. Increase variable d by your stepwidth dStepwidth inside the loop every iteration (I assume you forgot that step, when the loop doesn't end in your case).

d = d + dStepwidth;

Here is the while-loop version:

% mass of rectangular prism with a hole (cylinder) in it
clear, clc
rho = 2700;

W = 1;              % Width of rectangular prism
L = 2;              % Length of rectangular prism
d0 = 0.05;          % Initial diameter of the hole (cylinder)
dStepwidth = 0.1;   % Stepwidth of the diameter of the hole
dMax = W/2;         % Maximum diameter of the hole

d = d0;             % changing diameter              
while d <= dMax
    mass_prism = W^2 * L * rho;
    mass_hole = (pi * (d/2).^2 * L) * rho;
    mass_total = mass_prism - mass_hole;
    fprintf ( 'd = %0.3f m \nW = %0.1f m \nL = %0.1f m \nRho = %0.3f kg/m^3 \nm = %0.5f kg\n\n',...
        d, W, L, rho, mass_total);
    d = d + dStepwidth;
end