Activity 2: Crash Course on C

Michelle

Folder: activities_c_practice

This is an introduction to

• C programming basic constructs
• The representation of C integer data types

You will complete several tasks that ask you to practice with writing C code, including looking at how C on the server represents integer data.

• You will create a function to do a simple calculation, practicing with numbers, conditionals, assert, and printf
• You will create a function to experiment with C loop forms
• You will create a function to print the size in bytes of each C integer type, and to print the min and max values for each type
  • unsigned char, unsigned short, unsigned int, unsigned long
  • char, short, int, long

Hint: At the bottom of this README is a section called References that contains references to resources that can help you with these questions

Provided Code

There is one code file for this activity, as well as a Makefile:

• activity2.c
  • the source file which contains the main function, in which you will complete your tasks
• Makefile
  • a short makefile to automate the compilation process

Open the file activity2.c and read it carefully.

Notice that it has declarations of functions at the top of the file, followed by the main program, and then the function definitions themseles. There are "TODO" comments in the file to help guide you in this activity.

Open the file Makefile and read it carefully.

Recall that the Makefile defines how we compile our source code into an executable program, automating the process for us.

• At the top of the Makefile, we define the compiler we want to use, with one option, which chooses which variant of C to use (C99).

• The next line specifies a target (the text before a colon), and the files it depends on (listed after the colon).

  • The target is the file that will be generated, in this case the name of the executable (try_c)
  • The dependency files are the files that will be used to build the executable; if one of the dependency files has been modified, calling make with the given target will cause it to rerun the steps

• The indented line or lines that follow specify terminal commands to use to create the executable; in this case we call the compiler

• The first target in a file is the "default" target; when you call make by itself the default is checked and run (if necessary)

  make

The above command is the same as if you had typed:

make try_c

You will execute the program by typing this in the terminal:

./try_c

Try these commands in the terminal, and see what they do. What happens if you run make two times in a row?

When coding in C, you will do this over and over again in the terminal as you make changes to your code:

make 
./try_c

Remember that you can retrieve previous commands at the linux terminal shell by using the up arrow key many times. Try using the arrow keys now.

Your tasks

First Steps

• Open activity2.c in your editor
• Add your name(s) in a comment at the top of the file. You must put your name at the top of every code file you edit for assignments for this course (you will lose points on homework questions if you don't!)
• Also, add your name(s) to this README document: Some of you have Github usernames that are very different from your actual names. This makes it easier to know quickly who is who!

Task 1: A simple "sales tax" example

• Look for the definition of the sales_example function in activity2.c.
• Note how the function takes in 3 inputs: the cost per item, the number of items, and the sales tax rate.
• In the function, do the following:
  • Declare and define a variable to hold the total pre-tax amount to be paid (cost times number)
  • Declare and define a variable to hold the total cost after incorporating sales tax
  • Add an if statement to check if the sales tax rate is 0.0; it should print a message that no sales tax applies if this is the case
  • Regardless of the outcome of the if statement, return the total cost calculated
• Examine the call to sales_example in main; compile and run the program, checking that the output is correct
• Try a range of other values to ensure the correct result is returned each time
• Incorporate the assert statement to automatically check for correct results, testing at least 4 different scenarios

Task 2: Experimenting with loops

• Near the top of the file, add a declaration of a function called loop_example that returns nothing and that has no input parameters
• In the main function, add a call to your new function
• In the space provided below the main function, put in your definition of loop_example
  • First, write a simple for loop that loops over the integers from 10 to 25, going up by 5 each time, and it prints the integer and the square of the integer each time
  • Next, add a while loop that does the same thing
  • Finally, add a do-while loop that does the same thing

Task 3: Exploring sizes and ranges for unsigned integer types

• Read the starter code for the utype_sizes function: it prints a constant from the limits.h library for the maximum value of the unsigned char integer type, and it prints the number of bytes used by an unsigned char
• Using the resources listed in the References section below, research how to display a value of each of the three additional types we are examining: unsigned short, unsigned int, and unsigned long
• Also research the min/max constants provided by the limist.h library
• Add print statements for the three additional types, printing the maximum value for that type, and its number of bytes

Edit the table below to record the values you found!

Type	Max value	Number Bytes
unsigned char	255	1
unsigned short	65535	2
unsigned int	65535	4
unsigned long	65535	8

Task 4: Exploring sizes and ranges for signed integer types

• Near the top of the file, add a declaration for stype_sizes
• In the main function, add a call to stype_sizes
• In the space below main, add a definition of stype_sizes
  • Base this on utype_sizes: four print statements
  • Include the minimum as well as the maximum in each print statement
  • Research the different codes needed for signed integers

Edit the table below to record the values you found!

Type	Min value	Max value	Number Bytes
char
short
int
long

Notes

• The macro sizeof(TYPE) returns the number of bytes used for a particular data type by the compiler on the particular hardware where the program is compiled and run. The %zu code is used to print the result of sizeof!

Feeling stuck or confused?

Ask for help right away from neighbors, preceptors, or instructor!

Commenting as documentation

You should comment each function you write like you would for Java:

/** Describe inputs and return values and 
 * what the function does -- this comment
 * must start with /**, just like 
 * javadoc comments
 */

References

• Makefile guides
  • An Introduction to Makefiles, by GNU
  • Makefile Tutorials and Examples to Build From, by Aniket Bhattacharyea
  • makefile basics - anthony explains
• General C syntax help
  • Chapter 1 of Dive into Systems
  • The C Programming Language, often just known as K&R for Kernighan and Ritchie
  • C: A Reference Manual, by Harbison and Steele
• The assert statement
  • assert reference from cplusplus.com
• Printf formatting codes
  • printf format specifier reference from cplusplus.com.
  • Format Specifiers in C by The Crazy Programmer
• Limit constants
  • _C Programming/limits.h
  • limits.h reference in tutorialspoint