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, Revisited
  • Exercise 2: Limits
  • Exercise 3: Exceeding Limits
  • Exercise 4: Enumerated Types
  • Exercise 5: Fun with Characters
• For Those with Extra Time
  • Extra 1: ASCII

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 ~/csc161/labs/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, Revisited

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: 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);

Exercise 4: Enumerated Types

As you may have learned from section 2.3, C supports enumerated types, types in which you can name the values. To declare an enumerated type, you write,

enum typename { VAL0, VAL1, ... }

As I've tried to note, custom in C is to make the values all uppercase.

To declare a variable of that type, you write

enum typename variable;

For example, here is a complete (but pointless) program that defines a type for five popular Greek letters.

#include <stdio.h>

enum greek { ALPHA, BETA, GAMMA, DELTA, EPSILON };

int
main ()
{
  enum greek g;
  g = ALPHA;
  return 0;
} // main

a. Extend this program to print out the five values. Use a pattern of "%d" to print one of the values.

b. Determine what happens if you try to use "%s" to print the values.

Exercise 5: Fun with Characters

For each of the following expressions, predict the output and then experimentally check your answer. (You will need to embed the code in a program.)

Note that you can check the ASCII table with man ascii.

• printf ("abc\n");
• printf ("ab\bc\n");
• printf ("ab\fc\n");
• printf ("ab\nc\n");
• printf ("ab\rc\n");
• printf ("ab\tc\n");
• printf ("ab\vc\n");
• printf ("ab\\c\n");
• printf ("ab\?c\n");
• printf ("ab\'c\n");
• printf ("ab\"c\n");
• printf ("ab\050c\n");
• printf ("ab\x5e\n");

For Those with Extra Time

Extra 1: ASCII

Write a program that prints out a simple ASCII table of the decimal number of each character from 32 to 127.