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Upon running the file, the
output.txt file will display the following:
The radius of acetylene bottle: 0.3 meters
The height of cylindrical part of acetylene bottle: 1.5 metersThe volume of the acetylene bottle: 0.480664 cubic meters.
In programming, a loop executes a set of code a specified number of times or until a condition is met.
This loop iterates an index variable from an initial value using a specified increment to a final value and runs a set of code. The for loop syntax is the following:
for loop_index=vector_statement
code...
codeend
Calculate
for
using an increment of
.
for x=-pi:pi/4:pi
y=cos(x);fprintf('%8.3f %8.2f \n',x,y);
end
In the brief script above, is the loop index that is initiated from and incremented with to a final value of . At the end of each increment, is calculated and displayed with the fprintf command. This process continues until .
From a previous exercise we know \n creates a new line when included in the fprintf command. Here, we also use %8.3f to specify eight spaces and three decimal places for the first variable x. Likewise %8.2f specifies the formatting for the second variable y but in this case, y is displayed with two decimal places. The result is the following:
-3.142 -1.00
-2.356 -0.71-1.571 0.00
-0.785 0.710.000 1.00
0.785 0.711.571 0.00
2.356 -0.713.142 -1.00
We can improve our code by adding formatting lines as follows:
clear; clc;
fprintf(' x cos(x)\n') % title rowfprintf(' ----------------\n') % title row
for x=-pi:pi/4:pi % loop_index=inital_value:increment_value:final_valuey=cos(x); % code to calculate cos(x)
fprintf('%8.3f %8.2f \n',x,y); % code to print the output to screenend
Screen output:
x cos(x)
-----------------3.142 -1.00
-2.356 -0.71-1.571 0.00
-0.785 0.710.000 1.00
0.785 0.711.571 0.00
2.356 -0.713.142 -1.00
Like the for loop, a while loop executes blocks of code over and over again however it runs as long as the test condition remains true. The syntax of a while loop is
while test_condition
code...
codeend
Using a
while loop, calculate
for
using an increment of
.
This time we need to initialize the x value outside the loop and then state the test condition in the first line of the while loop. We also need to create an increment statement within the while loop:
x=-pi;
while x<=pi
y=cos(x);fprintf('%8.3f %8.2f \n',x,y);
x = x + (pi/4);end
The result is the same as that of the previous example:
-3.142 -1.00
-2.356 -0.71-1.571 0.00
-0.785 0.710.000 1.00
0.785 0.711.571 0.00
2.356 -0.713.142 -1.00
Now we can improve the code by adding extra formatting lines and comments:
clear; clc;
fprintf(' x cos(x)\n') % title rowfprintf(' ----------------\n') % title row
x=-pi; % initiating the x valuewhile x<=pi % stating the test condition
y=cos(x); % calculating the value of yfprintf('%8.3f %8.2f \n',x,y); % printing a and y
x = x + (pi/4); % iterating to the next stepend
The result should look the same as before.
x cos(x)
-----------------3.142 -1.00
-2.356 -0.71-1.571 0.00
-0.785 0.710.000 1.00
0.785 0.711.571 0.00
2.356 -0.713.142 -1.00
diary FunctionInstead of writing a script from scratch, we sometimes solve problems in the Command Window as if we are using a scientific calculator. The steps we perform in this fashion can be used to create an m-file. For example, the
diary function allows us to record a MATLAB session in a file and retrieve it for review. Reviewing the file and by copying relevant parts of it and pasting them in to an m-file, a script can be written easily.
Typing
diary at the MATLAB prompt toggles the diary mode on and off. As soon as the diary mode is turned on, a file called diary is created in the current directory. If you like to save that file with a specific name, say for example problem16, type
>>diary problem16.txt .
A file named problem16.txt will be created. The following is the content of a diary file called problem16.txt. Notice that in that session, the user is executing the four files we created earlier. The user's keyboard input and the resulting display output is recorded in the file. The session is ended by typing
diary which is printed in the last line. This might be useful to create a record of your work to hand in with a lab or to create the beginnings of an m-file.
AcetyleneBottle
Vol_total =0.4807
AcetyleneBottleInteractiveEnter the radius of acetylene bottle in meters .3
Enter the height of cylinderical part of acetylene bottle in meters 1.5Vol_total =
0.4807AcetyleneBottleInteractiveDisp
This script computes the volume of an acetylene bottleEnter the radius of acetylene bottle in meters .5
Enter the height of cylinderical part of acetylene bottle in meters 1.6The volume of the acetylene bottle is1.5184
AcetyleneBottleInteractiveDisp1This script computes the volume of an acetylene bottle:Enter the radius of acetylene bottle in meters .9
Enter the height of cylinderical part of acetylene bottle in meters 1.9The volume of the acetylene bottle is 6.3617 cubic meters.diary
Try to apply the following guidelines when writing your scripts:
input ,
disp and
num2str can be used to make scripts interactive,fopen ,
fprintf and
fclose functions are used to create output files,for loop is used to repeat a specific block of code a definite number of times.while loop is used to repeat a specific block of code an indefinite number of times, until a condition is met.diary function is useful to record a MATLAB command window session from which an m-file can be easily created,
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