Instructions to Students:

1.

Part I

While not required, it is suggested that this part should be done with all members of the team working at one computer; the team meeting coordinator should serve as the keyboard operator.

An important part of C programming to really understand is the increment and decrement operators as well as the prefix and postfix uses of these.  (Note: these should have been discussed in very recent lecture with the students.)

The increment operator (++) and the decrement operator (- -) can be applied to variables.  However they cannot be applied to constants or ordinary expressions.

When using the increment (or decrement) operator, the value of the variable in memory is altered.  This is different from normal usage of the + or – operators.  If you execute a+b, neither the value of a nor b is changed, however a++ changes the value of a.

Use the following code in a program that will get you on track to fully understand and appreciate the usages of these operators.

int a, b, c = 0;

a = ++c;

b = c++;

printf("%d %d %d\n", a, b, ++c);

Now, add to your program a block of code that will show that i += 1 is the same as i++.  Make another block that will go through a for loop that prints out the numbers 1-10.  (Note: Students should have done this a few weeks prior in class; however, tell them to use the increment operator this time.) Change this to a while loop in the next block. 

Take a few minutes to add two more blocks of code that will demonstrate a learning experience.  Comment within your code why each block is significant.  In total, your code should have 6 separate blocks of code.  Each should have a print statement to demonstrate the working of each code.

Name your file lab10_p1.c

TIMEKEEPER:  Your team should spend 20-30 minutes working with this section (this is only a guideline).  Remember that it is for your own understanding and that your team is mutually responsible for the information. 
 

2.

Part II

The idea of call by value is basically that you can pass a variable to a function and not lose the value of the variable through the function.

 Your task is to write a main program that will prompt a user for a magnitude and an angle (in degrees) for a vector, pass the angle (in degrees) and the magnitude to a function through the argument/parameter list. Upon returning from the function, the program should output the magnitude and angle of the vector (in degrees), as well as the value of the x component of the vector as shown below.  The function should convert the angle to radians (using the same variable name) and compute the x component of the vector, returning the value to the main program. 

Call your program lab10_p2.c.

The main function should have an output strongly resembling the below:

 % a.out

Enter an Angle:

45

Enter a Magnitude:

42

The x value of a vector with a magnitude of 42 and angle of 45 degrees is 29.69.

 TIMEKEEPER:  This exercise should take 15-25 minutes.  Remember this is only a guideline.
 

3.

Part III

(Note: Remind the students that they learned about arrays in their studies of Fortran.)  C (like most other high-level programming languages) also supports arrays.  However, the implementation is slightly different than what you saw in Fortran.  The most noticeable difference is the notation.  In C the first element of an array is denoted as element 0.  This will be the source of many, many errors—just a hint.

 Your task is to define a 10-element single subscripted integer array that is initialized (via the declaration statement) to contain the numbers 1 through 10 in elements 0 through 9, respectively.  The program should be written in such a way that it will repeatedly prompt the user to enter a specific element number of the array to be displayed on the computer monitor and then output the value stored in the element in a manner similar to the example shown below.  You should make use of the value returned by scanf() to control when input is to be terminated (recall: a carriage return followed by control-d should return a value of false from scanf).  

Name your file lab10_p3.c.

The output should look remarkably like this:

 % a.out

 Which element of the array would you like to have printed out?

2

The value of element 2 is 3

Which element of the array would you like to have printed out?

1

The value of element 1 is 2.

.ctrl-d

TIMEKEEPER:  This exercise should take between 15 and 20 minutes.  This is just a guideline.
 

4.

Part IV

This part should be done with all members of the team working at one computer; the team recorder should serve as the key-board operator.

 The scope of a variable refers to the part of the program for which the variable is known or accessible.  A variable is known throughout a block of code.  Variables are only available within the block of code where the variable is declared.  A variable is not carried through a function because it has separate declarations.

 The following code is legal.  Run it within a main program and see what happens.  Alter the code to more clearly express the intents of the programmer.  PLEASE NOTE: The following code does not express the coding practices of the administration of the course.  As a matter of fact, the code is considered very bad programming practice.  Consider this a learning experience.

 Name your code lab10_p4.c.

 We suggest that you take your time to really see what happens when you alter this code.  Add a function and play with variable names. 

             {

               int a = 2;

              printf("%d\n", a);

             {

                       int a = 7; 

                       printf("%d\n", a);

                }

               printf("%d\n", ++a);

                }

 TIMEKEEPER:  This exercise should take between 10 and 15 minutes.  This is only a guideline. 
 

5.

Part V

The product of two matrices is represented as [c] = [a][b], where the elements of [c] are defined as:

 where n equals the column dimension of [a] and the row dimension [b].  That is, the element is obtained by adding the product of individual elements from the i^th row of the first matrix, in this case [a], by the j^th column of the second matrix [b].

 According to this definition, multiplication of two matrices can only be performed if the first matrix has as many columns as the number of rows in the second matrix.  Thus, if [a] is an m-by-n matrix, [b] could be and n-by-l matrix.  For this case the resulting [c] matrix would have dimension of m-by-l.  However, if [b] were a l-by-n matrix, the multiplication could not be performed.

 As a team, write a flowchart for an algorithm that will ask a user to enter all the elements for two real matrices (since this is an algorithm we use the term matrices, not arrays): a that is of order (mxn) and b that is of order (nxl).  The algorithm, should then take the product of the two matrices, storing the result in a new matrix called c (which is of order (mxl)), using the definition of matrix multiplication shown above.  Develop a simple test case by hand to ensure that your algorithm works before you attempt to actually write a program.

 After verifying your algorithm, convert it to an appropriate C program. It is safe to assume that the input matrices will not be larger than 10 by 10, however a #define should be used to ensure that this value can be easily changed later.  Name your file lab10_p5.c

 TIMEKEEPER:  This should take between 20 and 25 minutes.  Turn in your team's flowchart and hand-test case to your instructor or TA.
 

6.

Turn in the following files by (insert date) to: (insert name)

·         lab10_p1.c

·         lab10_p2.c

·         lab10_p3.c

·         lab10_p4.c

·         lab10_p5.c
 

7.

Individual Check for Understanding

Complete the handout.