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num2str FunctionThe
num2str function allows us to convert a number to a text string. Basic syntax is
str = num2str(A) where variable A is converted to a text and stored in
str . Let's see how it works in
AcetyleneBottleInteractiveDisp.m . Remember to save the file with a different name before editing it, for example,
AcetyleneBottleInteractiveDisp1.m .
Add the following line of code to your file:
str = ['The volume of the acetylene bottle is ', num2str(Vol_total), ' cubic meters.'];
Notice that the three arguments in
str are separated with commas. The first argument is a simple text that is contained in ' '. The second argument is where the number to string conversion take place. And finally the third argument is also a simple text that completes the sentence displayed on the screen. Using semicolon at the end of the line suppresses the output. In the next line of our script, we will call
str with
disp(str); .
AcetyleneBottleInteractiveDisp1.m file should look like this:
% This script computes the volume of an acetylene bottle
% user is prompted to enter% a radius r for a hemispherical top
% a height h for a cylindrical partclc % Clear screen
disp('This script computes the volume of an acetylene bottle:')disp(' ') % Display blank line
r=input('Enter the radius of acetylene bottle in meters ');h=input('Enter the height of cylindrical part of acetylene bottle in meters ');
Vol_top=(2*pi*r^3)/3; % Calculating the volume of hemispherical top [m3]Vol_cyl=pi*r^2*h; % Calculating the volume of cylindrical bottom [m3]
Vol_total=Vol_top+Vol_cyl; % Calculating the total volume of acetylene bottle [m3]disp(' ') % Display blank line
str = ['The volume of the acetylene bottle is ', num2str(Vol_total), ' cubic meters.'];
disp(str);
Running the script should produce the following:
This script computes the volume of an acetylene bottle:Enter the radius of acetylene bottle in meters .3
Enter the height of cylindrical part of acetylene bottle in meters 1.5The volume of the acetylene bottle is 0.48066 cubic meters. fopen And
fclose FunctionsThe first command is used to open or create a file. The basic syntax for
fopen is as follows:
fid = fopen(filename, permission)
For example,
fo = fopen('output.txt', 'w'); opens or creates a new file named
output.txt and sets the permission for writing. If the file already exists, it discards the existing contents.
fclose command is used to close a file. For example, if we type in
fclose(fo); , we close the file that was created above.
fprintf Function
fprintf function writes formatted data to the computer monitor or a file. This command can be used to save the results of a calculation to a file. To do this, first we create or open an output file with
fopen , second we issue the
fprintf command and then we close the output file with
fclose .
The simplified syntax for
fprintf is as follows:
fprintf=(fid, format, variable1, variable 2, ...)
Add the following lines to your .m file:
fo = fopen('output.txt', 'w');
fprintf(fo,'The radius of acetylene bottle: %g meters \n', r);fprintf(fo,'The height of cylindrical part of acetylene bottle: %g meters \n', h);
fprintf(fo,'The volume of the acetylene bottle: %g cubic meters. \n', Vol_total);fclose(fo);
Here, we first create the
output.txt file that will contain the following three variables
r,
h and
Vol_total . In the
fo output file, the variables are formated with
%g which automatically uses the shortest display format. You can also use
%i or
%d for integers and
%e for scientific notation. In our script above, the
\n (newline) moves the cursor to the next line.
Naming the new .m file as
AcetyleneBottleInteractiveOutput.m , it should look like this:
% This script computes the volume of an acetylene bottle
% user is prompted to enter% a radius r for a hemispherical top
% a height h for a cylindrical partclc % Clear screen
disp('This script computes the volume of an acetylene bottle:')disp(' ') % Display blank line
r=input('Enter the radius of acetylene bottle in meters ');h=input('Enter the height of cylindrical part of acetylene bottle in meters ');
Vol_top=(2*pi*r^3)/3; % Calculating the volume of hemispherical top [m3]Vol_cyl=pi*r^2*h; % Calculating the volume of cylindrical bottom [m3]
Vol_total=Vol_top+Vol_cyl; % Calculating the total volume of acetylene bottle [m3]disp(' ') % Display blank line
str = ['The volume of the acetylene bottle is ', num2str(Vol_total), ' cubic meters.'];
disp(str);fo = fopen('output.txt', 'w');
fprintf(fo,'The radius of acetylene bottle: %g meters \n', r);fprintf(fo,'The height of cylindrical part of acetylene bottle: %g meters \n', h);
fprintf(fo,'The volume of the acetylene bottle: %g cubic meters. \n', Vol_total);fclose(fo); 
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