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: Coercion
  • Exercise 2: Enumerated Types
  • Exercise 3: Incrementing

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/MoreTypes/, 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: 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 2: 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 3: Incrementing

You've learned that the ++ operation increments its parameter. You've also learned that you can place it before or after a variable. What's the difference? Let's check.

a. Predict the output of the following chunk of code.

  int x = 5;
  printf ("x = %d\n", x);
  printf ("x++ = %d\n", x++);
  printf ("x = %d\n", x);
  printf ("++x = %d\n", ++x);
  printf ("x = %d\n", x);

b. Check your answer experimentally.

c. Predict the output of the following chunk of code.

  int y = 6;
  printf ("%d %d %d %d\n", y++, y++, y++, y++);

d. Check your answer experimentally.

e. Discuss the meaning of your output.