Laboratory: Types in C

Summary: We explore basics of types in C.

Prerequisites: Familiarity with basic Linux commands. Ability to use an editor. Ability to compile C files.

• Preparation
• Exercises
  • Exercise 1: Compiling Basics
  • Exercise 2: Limits
  • Exercise 3: Coercion
  • Exercise 4: Enumerated Types
  • Exercise 5: Exceeding Limits

Preparation

a. Log in to your MathLAN workstation. (Of course, you've probably already done that if you're reading this laboratory.)

b. Open a terminal window into which you can type commands.

c. Create a directory for this lab. (I'd suggest something like ~/Courses/CSC161/Types/, but it's up to you.)

d. In that directory, create a file called Makefile that contains the following line.

CFLAGS=-Wall

Exercises

Exercise 1: Compiling Basics

a. Create your own copy of the Hello World program, storing it in the file hello.c.

b. Confirm that you can compile the program use make.

c. Confirm that you can check the program using splint.

Exercise 2: Limits

Using <limits.h> (documented on page 257 of K&R), find the various interesting limits on integer-like types. A typical line of your program will look something like the following.

  printf ("CHAR_BIT  %12d\n", CHAR_BIT);

Exercise 3: Coercion

Determine experimentally, what happens when

• You assign a character to an integer.
• You assign an integer to a character.
  • When the integer is in the range 0..127
  • When the integer is negative.
  • When the integer is greater than 256.
• You assign a long to a short.
• Anything else you think might be interesting.

For example, to explore the assignment of a long to a short, you might write

  long l;
  short s;
  ...
  l = SHRT_MAX + 5;
  s = l;

  printf ("Long: %ld\n", l);
  printf ("Short: %d\n", s);

Exercise 4: Enumerated Types

Consider the following code:

enum values { ALPHA, BETA, GAMMA };

int
main ()
{
  int i;
  enum values v;

  i = BETA;
  v = 23;
}

a. What do you expect the compiler to do if you attempt to compile this code? (Assume that you're using -Wall.

b. Check your answer experimentally.

c. What do you expect splint to report for this code?

d. Check your answer experimentlaly.

e. What value do you expect i to have when you print it out?

f. Check your answer experimentally.

Exercise 5: Exceeding Limits

Predict the results of each of the following and then check your answers experimentally. (Note that we will explore why you get these results when we talk about binary representation.)

Assume that we've declared i as an integer variable.

a.

  i = INT_MIN;
  --i;
  printf ("i = %d\n", i);

b.

  i = INT_MAX;
  ++i;
  printf ("i = %d\n", i);

c.

  i = -31;
  i = abs (i);
  printf ("i = %d\n", i);

d.

  i = INT_MIN;
  i = abs (i);
  printf ("i = %d\n", i);

e.

  i = INT_MAX / 4;
  printf ("i = %d\n", i);

f.

  i = INT_MAX / 4;
  i = i*5;
  printf ("i = %d\n", i);